diff --git a/changelog.d/rebind-holders-after-reform.fixed.md b/changelog.d/rebind-holders-after-reform.fixed.md
new file mode 100644
index 000000000..1f4da5a92
--- /dev/null
+++ b/changelog.d/rebind-holders-after-reform.fixed.md
@@ -0,0 +1 @@
+Simulation.apply_reform now rebinds existing holders to each branch's system before clearing cached calculations.
diff --git a/policyengine_core/simulations/simulation.py b/policyengine_core/simulations/simulation.py
index de5824c59..9b1ffc3a4 100644
--- a/policyengine_core/simulations/simulation.py
+++ b/policyengine_core/simulations/simulation.py
@@ -932,6 +932,8 @@ def apply_reform(self, reform: Union[tuple, Reform]):
             if isinstance(reform, dict):
                 reform = Reform.from_dict(reform)
             reform.apply(self.tax_benefit_system)
+        # Refresh holders before input replay looks them up in the new system.
+        self._bind_to_tax_benefit_system()
         # Invalidate every cached value so the simulation recomputes under
         # the new tax-benefit system. Previously ``apply_reform`` left
         # ``_fast_cache``, in-memory holder storage, and on-disk holder
@@ -1318,6 +1320,11 @@ def _bind_to_tax_benefit_system(self) -> None:
         holder was built for the reform's definition in a way a new variable
         cannot change: in another entity's population, or with storage for
         (or not for) an ``ETERNITY`` variable.
+
+        After an in-place reform, compatible holders keep their storage and
+        recorded inputs. Each existing branch binds to its own system, so
+        shared-system branches follow the reform and a baseline keeps its
+        baseline variables.
         """
         system = self.tax_benefit_system
         if system is None:
@@ -1346,7 +1353,11 @@ def _bind_to_tax_benefit_system(self) -> None:
                     holder.variable = variable
 
         def kept(name):
-            return name in variables and name not in dropped
+            # A reform may supply a new entity's input before we drop the old holder.
+            return name in variables and (
+                name not in dropped
+                or name in self.populations[variables[name].entity.key]._holders
+            )
 
         if getattr(self, "_user_input_keys", None) is not None:
             self._user_input_keys = {
@@ -1354,6 +1365,8 @@ def kept(name):
             }
         if getattr(self, "input_variables", None) is not None:
             self.input_variables = [name for name in self.input_variables if kept(name)]
+        for branch in self.branches.values():
+            branch._bind_to_tax_benefit_system()
 
     def create_shortcuts(self) -> None:
         for _key, population in self.populations.items():
diff --git a/tests/core/test_apply_reform_holders.py b/tests/core/test_apply_reform_holders.py
new file mode 100644
index 000000000..888d24a69
--- /dev/null
+++ b/tests/core/test_apply_reform_holders.py
@@ -0,0 +1,295 @@
+"""Reforms refresh existing holders without discarding compatible inputs."""
+
+import numpy as np
+import pytest
+
+from policyengine_core.errors import VariableNotFoundError
+from policyengine_core.parameters import ParameterNode
+from policyengine_core.periods import ETERNITY, YEAR, period
+from policyengine_core.reforms import Reform
+from policyengine_core.variables import Variable
+from tests.fixtures.reform_holders import (
+    Household,
+    Person,
+    build,
+    change_default,
+    store_on_disk,
+)
+
+PERIOD = "2025"
+
+
+def assert_bound(simulation):
+    for population in simulation.populations.values():
+        for name, holder in population._holders.items():
+            assert holder.variable is simulation.tax_benefit_system.variables[name]
+            assert holder.variable.entity.key == population.entity.key
+            assert holder._memory_storage.is_eternal == (
+                holder.variable.definition_period == ETERNITY
+            )
+
+
+def test_defined_for_default_does_not_depend_on_other_people():
+    results = []
+    for mask in ([False], [False, True]):
+        simulation = build(mask)
+        old_holder = simulation.get_holder("award")
+        simulation.apply_reform(change_default(20))
+        results.append(simulation.calculate("award", PERIOD).tolist())
+        assert simulation.get_holder("award") is old_holder
+
+    assert results == [[20], [20, 100]]
+
+
+@pytest.mark.parametrize("on_disk", [False, True])
+def test_replaced_variable_keeps_recorded_inputs(on_disk):
+    simulation = build()
+    if on_disk:
+        store_on_disk(simulation, "award")
+    simulation.set_input("award", PERIOD, [7, 9])
+    holder = simulation.get_holder("award")
+    records = simulation._user_input_keys.copy()
+    simulation.input_variables = ["award", "eligible"]
+
+    simulation.apply_reform(change_default(20))
+
+    assert simulation.get_holder("award") is holder
+    assert_bound(simulation)
+    assert simulation._user_input_keys == records
+    assert simulation.input_variables == ["award", "eligible"]
+    np.testing.assert_array_equal(simulation.calculate("award", PERIOD), [7, 9])
+    np.testing.assert_array_equal(holder._get_array_from_storage(PERIOD), [7, 9])
+
+
+class NeutralizeAward(Reform):
+    def apply(self):
+        self.neutralize_variable("award")
+
+
+@pytest.mark.parametrize("on_disk", [False, True])
+def test_neutralized_variable_keeps_input_storage_but_reads_its_default(on_disk):
+    simulation = build()
+    if on_disk:
+        store_on_disk(simulation, "award")
+    simulation.set_input("award", PERIOD, [7, 9])
+    records = simulation._user_input_keys.copy()
+
+    simulation.apply_reform(NeutralizeAward)
+
+    holder = simulation.get_holder("award")
+    assert_bound(simulation)
+    assert holder.variable.is_neutralized
+    assert simulation._user_input_keys == records
+    np.testing.assert_array_equal(holder._get_array_from_storage(PERIOD), [7, 9])
+    np.testing.assert_array_equal(simulation.calculate("award", PERIOD), [0, 0])
+
+
+class added(Variable):
+    value_type = float
+    entity = Person
+    definition_period = YEAR
+    default_value = 13
+    label = "Added amount"
+
+
+class AddAndRemove(Reform):
+    def apply(self):
+        self.add_variable(added)
+        del self.variables["annual_value"]
+
+
+@pytest.mark.parametrize("on_disk", [False, True])
+def test_added_variable_is_lazy_and_removed_variable_drops_holder_and_inputs(on_disk):
+    simulation = build()
+    if on_disk:
+        store_on_disk(simulation, "annual_value")
+    simulation.set_input("annual_value", PERIOD, [7, 9])
+    simulation.input_variables = ["annual_value", "eligible"]
+
+    simulation.apply_reform(AddAndRemove)
+
+    assert_bound(simulation)
+    assert "annual_value" not in simulation.persons._holders
+    assert "annual_value" not in simulation.input_variables
+    assert all(key[0] != "annual_value" for key in simulation._user_input_keys)
+    with pytest.raises(VariableNotFoundError):
+        simulation.get_holder("annual_value")
+    assert "added" not in simulation.persons._holders
+    np.testing.assert_array_equal(simulation.calculate("added", PERIOD), [13, 13])
+    assert_bound(simulation)
+
+
+def test_tuple_reform_rebinds_after_each_reform():
+    class CheckFirstReform(Reform):
+        def apply(self):
+            assert (
+                self.simulation.get_holder("award").variable is self.variables["award"]
+            )
+            change_default(30).apply(self)
+
+    simulation = build([False])
+    simulation.apply_reform((change_default(20), CheckFirstReform))
+
+    assert_bound(simulation)
+    np.testing.assert_array_equal(simulation.calculate("award", PERIOD), [30])
+
+
+def test_dict_reform_keeps_inputs_and_rebinds_stale_holders():
+    simulation = build([False])
+    simulation.tax_benefit_system.parameters = ParameterNode(
+        "", data={"amount": {"values": {"2025-01-01": {"value": 1}}}}
+    )
+    simulation.set_input("income", PERIOD, [7])
+    change_default(20).apply(simulation.tax_benefit_system)
+
+    simulation.apply_reform({"amount": {"2025": 2}})
+
+    assert_bound(simulation)
+    assert simulation.tax_benefit_system.parameters("2025-01-01").amount == 2
+    np.testing.assert_array_equal(simulation.calculate("income", PERIOD), [7])
+    np.testing.assert_array_equal(simulation.calculate("award", PERIOD), [20])
+
+
+def test_existing_baseline_keeps_its_own_system():
+    simulation = build([False])
+    baseline = simulation.get_branch("baseline", clone_system=True)
+    simulation.baseline = baseline
+    baseline_system = baseline.tax_benefit_system
+    np.testing.assert_array_equal(baseline.calculate("award", PERIOD), [0])
+
+    simulation.apply_reform(change_default(20))
+
+    assert simulation.baseline is baseline
+    assert baseline.tax_benefit_system is baseline_system
+    assert_bound(simulation)
+    assert_bound(baseline)
+    np.testing.assert_array_equal(baseline.calculate("award", PERIOD), [0])
+    np.testing.assert_array_equal(simulation.calculate("award", PERIOD), [20])
+
+
+def test_existing_branches_rebind_to_their_own_systems():
+    simulation = build([False])
+    shared = simulation.get_branch("shared")
+    nested = shared.get_branch("nested")
+    independent = simulation.get_branch("independent", clone_system=True)
+    independent.apply_reform(change_default(40))
+    for branch in (simulation, shared, nested, independent):
+        branch.set_input("income", PERIOD, [7])
+        branch.calculate("award", PERIOD)
+
+    simulation.apply_reform(change_default(20))
+
+    for branch, expected in (
+        (simulation, 20),
+        (shared, 20),
+        (nested, 20),
+        (independent, 40),
+    ):
+        assert_bound(branch)
+        np.testing.assert_array_equal(branch.calculate("award", PERIOD), [expected])
+        np.testing.assert_array_equal(branch.calculate("income", PERIOD), [7])
+
+
+class MoveAnnualToHousehold(Reform):
+    def apply(self):
+        class annual_value(Variable):
+            entity = Household
+            default_value = 17
+
+        self.update_variable(annual_value)
+
+
+def test_entity_change_drops_orphaned_holder_and_input_records():
+    simulation = build()
+    simulation.set_input("annual_value", PERIOD, [7, 9])
+    simulation.input_variables = ["annual_value", "eligible"]
+
+    simulation.apply_reform(MoveAnnualToHousehold)
+
+    assert "annual_value" not in simulation.persons._holders
+    assert "annual_value" not in simulation.input_variables
+    assert all(key[0] != "annual_value" for key in simulation._user_input_keys)
+    np.testing.assert_array_equal(simulation.calculate("annual_value", PERIOD), [17])
+    assert_bound(simulation)
+
+
+@pytest.mark.parametrize("on_disk", [False, True])
+def test_entity_change_keeps_inputs_supplied_to_the_new_holder(on_disk):
+    class MoveAndSupply(Reform):
+        def apply(self):
+            MoveAnnualToHousehold.apply(self)
+            self.simulation.set_input("annual_value", PERIOD, [31])
+
+    simulation = build()
+    if on_disk:
+        store_on_disk(simulation, "annual_value")
+    simulation.set_input("annual_value", PERIOD, [7, 9])
+    simulation.input_variables = ["annual_value", "eligible"]
+
+    simulation.apply_reform(MoveAndSupply)
+
+    assert "annual_value" not in simulation.persons._holders
+    assert "annual_value" in simulation.input_variables
+    assert ("annual_value", "default", period(PERIOD)) in simulation._user_input_keys
+    np.testing.assert_array_equal(simulation.calculate("annual_value", PERIOD), [31])
+    assert_bound(simulation)
+
+
+class MakeAnnual(Reform):
+    def apply(self):
+        class eternal_value(Variable):
+            definition_period = YEAR
+
+            def formula(person, period):
+                return person.filled_array(period.start.year)
+
+        self.update_variable(eternal_value)
+
+
+class MakeEternal(Reform):
+    def apply(self):
+        class annual_value(Variable):
+            definition_period = ETERNITY
+
+        self.update_variable(annual_value)
+
+
+@pytest.mark.parametrize("on_disk", [False, True])
+def test_eternity_to_year_drops_incompatible_storage_and_inputs(on_disk):
+    simulation = build()
+    if on_disk:
+        store_on_disk(simulation, "eternal_value")
+    simulation.set_input("eternal_value", PERIOD, [7, 9])
+    simulation.input_variables = ["eternal_value", "eligible"]
+
+    simulation.apply_reform(MakeAnnual)
+
+    np.testing.assert_array_equal(
+        simulation.calculate("eternal_value", "2025"), [2025, 2025]
+    )
+    np.testing.assert_array_equal(
+        simulation.calculate("eternal_value", "2026"), [2026, 2026]
+    )
+    assert "eternal_value" not in simulation.input_variables
+    assert all(key[0] != "eternal_value" for key in simulation._user_input_keys)
+    assert_bound(simulation)
+
+
+@pytest.mark.parametrize("on_disk", [False, True])
+def test_year_to_eternity_uses_eternal_storage_for_new_inputs(on_disk):
+    simulation = build()
+    if on_disk:
+        store_on_disk(simulation, "annual_value")
+    simulation.set_input("annual_value", PERIOD, [7, 9])
+    simulation.apply_reform(MakeEternal)
+
+    assert all(key[0] != "annual_value" for key in simulation._user_input_keys)
+    simulation.set_input("annual_value", PERIOD, [11, 12])
+
+    assert_bound(simulation)
+    np.testing.assert_array_equal(
+        simulation.calculate("annual_value", "2025"), [11, 12]
+    )
+    np.testing.assert_array_equal(
+        simulation.calculate("annual_value", "2026"), [11, 12]
+    )
diff --git a/tests/core/test_apply_reform_holders_property.py b/tests/core/test_apply_reform_holders_property.py
new file mode 100644
index 000000000..be7b498e6
--- /dev/null
+++ b/tests/core/test_apply_reform_holders_property.py
@@ -0,0 +1,226 @@
+"""Check holder identity, defaults and recorded inputs after a reform."""
+
+import numpy as np
+import pytest
+
+hypothesis = pytest.importorskip("hypothesis")
+st = hypothesis.strategies
+
+from policyengine_core import periods
+from policyengine_core.reforms import Reform
+from policyengine_core.variables import Variable
+from tests.fixtures.reform_holders import YEAR, build, change_default, store_on_disk
+
+pytestmark = pytest.mark.filterwarnings(
+    "ignore:Memory configuration:policyengine_core.warnings.MemoryConfigWarning"
+)
+
+PROPERTY_SETTINGS = hypothesis.settings(max_examples=50, deadline=None, database=None)
+MASKS = st.lists(st.booleans(), min_size=1, max_size=6)
+DEFAULTS = st.integers(min_value=-1_000, max_value=1_000)
+REPLACED = ("award", "annual_value", "group_value")
+
+
+def assert_holder_identity(simulation):
+    for population in simulation.populations.values():
+        for name, holder in population._holders.items():
+            assert holder.variable is simulation.tax_benefit_system.variables[name]
+
+
+def expected_award(mask, default):
+    return np.where(mask, 100.0, float(default))
+
+
+def change_several_defaults(default):
+    class ChangeSeveralDefaults(Reform):
+        def apply(self):
+            for offset, name in enumerate(REPLACED):
+                attributes = {"default_value": float(default + offset)}
+                if name == "award":
+                    attributes["defined_for"] = "eligible"
+                self.update_variable(type(name, (Variable,), attributes))
+
+    return ChangeSeveralDefaults
+
+
+@PROPERTY_SETTINGS
+@hypothesis.given(
+    mask=MASKS,
+    default=DEFAULTS,
+    order=st.permutations(REPLACED),
+    warm=st.booleans(),
+    branches=st.sampled_from(("none", "shared", "independent", "both")),
+)
+@hypothesis.example(
+    mask=[False, True],
+    default=7,
+    order=("group_value", "award", "annual_value"),
+    warm=True,
+    branches="both",
+)
+def test_every_existing_holder_uses_its_system_variable(
+    mask, default, order, warm, branches
+):
+    simulation = build(mask)
+    for name in REPLACED:
+        population = simulation.get_variable_population(name)
+        del population._holders[name]
+    for name in order:
+        simulation.get_holder(name)
+        if warm:
+            simulation.calculate(name, YEAR)
+    related = []
+    if branches in ("shared", "both"):
+        related.append((simulation.get_branch("shared"), default))
+    if branches in ("independent", "both"):
+        related.append((simulation.get_branch("independent", clone_system=True), 0))
+
+    simulation.apply_reform(change_several_defaults(default))
+
+    for member in [simulation, *(branch for branch, _ in related)]:
+        assert_holder_identity(member)
+    for member, expected_default in [(simulation, default), *related]:
+        np.testing.assert_array_equal(
+            member.calculate("award", YEAR), expected_award(mask, expected_default)
+        )
+    np.testing.assert_array_equal(
+        simulation.calculate("annual_value", YEAR),
+        np.full(len(mask), default + 1),
+    )
+    np.testing.assert_array_equal(
+        simulation.calculate("group_value", YEAR), [default + 2]
+    )
+
+
+@PROPERTY_SETTINGS
+@hypothesis.given(mask=MASKS, default=DEFAULTS, warm=st.booleans())
+@hypothesis.example(mask=[False, False], default=7, warm=False)
+@hypothesis.example(mask=[False, True], default=7, warm=True)
+def test_person_result_does_not_depend_on_other_people(mask, default, warm):
+    combined = build(mask)
+    if warm:
+        combined.calculate("award", YEAR)
+    reform = change_default(default)
+    combined.apply_reform(reform)
+    together = combined.calculate("award", YEAR)
+    alone = []
+    for eligible in mask:
+        individual = build([eligible])
+        if warm:
+            individual.calculate("award", YEAR)
+        individual.apply_reform(reform)
+        alone.append(individual.calculate("award", YEAR)[0])
+
+    np.testing.assert_array_equal(together, expected_award(mask, default))
+    np.testing.assert_array_equal(alone, expected_award(mask, default))
+    np.testing.assert_array_equal(together, alone)
+
+
+@PROPERTY_SETTINGS
+@hypothesis.given(mask=MASKS, default=DEFAULTS, warm=st.booleans())
+@hypothesis.example(mask=[False, False], default=7, warm=True)
+@hypothesis.example(mask=[False, True], default=7, warm=False)
+def test_reform_before_or_after_holder_creation_returns_same_values(
+    mask, default, warm
+):
+    before_holder = build(mask)
+    del before_holder.person._holders["award"]
+    after_holder = build(mask)
+    if warm:
+        after_holder.calculate("award", YEAR)
+    reform = change_default(default)
+
+    before_holder.apply_reform(reform)
+    after_holder.apply_reform(reform)
+
+    expected = expected_award(mask, default)
+    np.testing.assert_array_equal(before_holder.calculate("award", YEAR), expected)
+    np.testing.assert_array_equal(after_holder.calculate("award", YEAR), expected)
+    assert_holder_identity(before_holder)
+    assert_holder_identity(after_holder)
+
+
+INPUT_ROWS = st.lists(
+    st.tuples(
+        st.booleans(),
+        st.integers(min_value=-10_000, max_value=10_000),
+        st.integers(min_value=-10_000, max_value=10_000),
+    ),
+    min_size=1,
+    max_size=6,
+)
+
+
+@PROPERTY_SETTINGS
+@hypothesis.given(
+    rows=INPUT_ROWS,
+    defaults=st.lists(DEFAULTS, min_size=1, max_size=4),
+    on_disk=st.booleans(),
+    branch=st.booleans(),
+)
+@hypothesis.example(
+    rows=[(False, 12, 34), (True, -5, 9)],
+    defaults=[7, 11],
+    on_disk=True,
+    branch=True,
+)
+def test_unchanged_recorded_inputs_survive_reforms(rows, defaults, on_disk, branch):
+    mask, incomes, eternal = zip(*rows)
+    simulation = build(mask)
+    if on_disk:
+        store_on_disk(simulation, "income", "annual_value", "eternal_value")
+    supplied = {
+        "income": np.asarray(incomes, dtype=np.float32),
+        "annual_value": np.asarray(incomes, dtype=np.float32) + 1,
+        "eternal_value": np.asarray(eternal, dtype=np.float32),
+    }
+    for name, values in supplied.items():
+        simulation.set_input(name, YEAR, values)
+        if on_disk:
+            holder = simulation.get_holder(name)
+            assert holder._disk_storage.get(periods.period(YEAR)) is not None
+            assert holder._memory_storage.get(periods.period(YEAR)) is None
+    members = [simulation]
+    if branch:
+        members.append(simulation.get_branch("existing"))
+    input_keys = [set(member._user_input_keys) for member in members]
+
+    for default in defaults:
+        simulation.apply_reform(change_default(default))
+        for member, keys in zip(members, input_keys):
+            assert member._user_input_keys == keys
+            for name, expected in supplied.items():
+                np.testing.assert_array_equal(member.calculate(name, YEAR), expected)
+            np.testing.assert_array_equal(
+                member.calculate("award", YEAR), expected_award(mask, default)
+            )
+            assert_holder_identity(member)
+
+
+@PROPERTY_SETTINGS
+@hypothesis.given(mask=MASKS, default=DEFAULTS, warm=st.booleans())
+@hypothesis.example(mask=[False, False], default=7, warm=True)
+@hypothesis.example(mask=[False, True], default=7, warm=False)
+def test_applying_same_reform_object_twice_returns_same_values(mask, default, warm):
+    once = build(mask)
+    twice = build(mask)
+    inputs = np.arange(len(mask), dtype=np.float32) + 5
+    for simulation in (once, twice):
+        simulation.set_input("income", YEAR, inputs)
+        if warm:
+            simulation.calculate("award", YEAR)
+    reform = change_default(default)
+
+    once.apply_reform(reform)
+    twice.apply_reform(reform)
+    twice.calculate("award", YEAR)
+    twice.apply_reform(reform)
+
+    expected = expected_award(mask, default)
+    for simulation in (once, twice):
+        np.testing.assert_array_equal(simulation.calculate("award", YEAR), expected)
+        np.testing.assert_array_equal(simulation.calculate("income", YEAR), inputs)
+        assert_holder_identity(simulation)
+    np.testing.assert_array_equal(
+        twice.calculate("award", YEAR), once.calculate("award", YEAR)
+    )
diff --git a/tests/fixtures/reform_holders.py b/tests/fixtures/reform_holders.py
new file mode 100644
index 000000000..65687bcab
--- /dev/null
+++ b/tests/fixtures/reform_holders.py
@@ -0,0 +1,115 @@
+"""Build small simulations for reforms applied after holders exist."""
+
+from policyengine_core import periods
+from policyengine_core.entities import Entity, GroupEntity
+from policyengine_core.experimental import MemoryConfig
+from policyengine_core.parameters import ParameterNode
+from policyengine_core.reforms import Reform
+from policyengine_core.simulations import Simulation
+from policyengine_core.taxbenefitsystems import TaxBenefitSystem
+from policyengine_core.variables import Variable
+
+YEAR = "2025"
+Person = Entity("person", "persons", "Person", "")
+Household = GroupEntity(
+    "household",
+    "households",
+    "Household",
+    "",
+    roles=[{"key": "member", "plural": "members"}],
+)
+
+
+class eligible(Variable):
+    value_type = bool
+    entity = Person
+    definition_period = periods.YEAR
+    label = "Eligibility"
+
+
+class award(Variable):
+    value_type = float
+    entity = Person
+    definition_period = periods.YEAR
+    default_value = 0
+    defined_for = "eligible"
+    label = "Award"
+
+    def formula(person, period):
+        return person.filled_array(100)
+
+
+class income(Variable):
+    value_type = float
+    entity = Person
+    definition_period = periods.YEAR
+    label = "Income"
+
+
+class annual_value(Variable):
+    value_type = float
+    entity = Person
+    definition_period = periods.YEAR
+    label = "Annual value"
+
+
+class eternal_value(Variable):
+    value_type = float
+    entity = Person
+    definition_period = periods.ETERNITY
+    label = "Eternal value"
+
+
+class group_value(Variable):
+    value_type = float
+    entity = Household
+    definition_period = periods.YEAR
+    label = "Group value"
+
+
+def build(mask=(False, True)):
+    """Put everyone in one household and record each person's eligibility."""
+    system = TaxBenefitSystem([Person, Household])
+    system.add_variables(
+        eligible, award, income, annual_value, eternal_value, group_value
+    )
+    system.parameters = ParameterNode(
+        "", data={"amount": {"values": {"2025-01-01": 1}}}
+    )
+    names = [f"p{index}" for index in range(len(mask))]
+    return Simulation(
+        tax_benefit_system=system,
+        situation={
+            "persons": {
+                name: {"eligible": {YEAR: bool(value)}}
+                for name, value in zip(names, mask)
+            },
+            "households": {"h": {"members": names}},
+        },
+    )
+
+
+def change_default(value):
+    """Return a reform that replaces the award's default with ``value``."""
+
+    class ChangeDefault(Reform):
+        def apply(self):
+            self.update_variable(
+                type(
+                    "award",
+                    (Variable,),
+                    {"default_value": float(value), "defined_for": "eligible"},
+                )
+            )
+
+    return ChangeDefault
+
+
+def store_on_disk(simulation, *names):
+    """Store future writes to the named holders on disk."""
+    simulation.memory_config = MemoryConfig(max_memory_occupation=0)
+    for name in names:
+        holder = simulation.get_holder(name)
+        if holder._disk_storage is None:
+            holder._disk_storage = holder.create_disk_storage()
+        holder._on_disk_storable = True