diff --git a/src/operation/problem_template.jl b/src/operation/problem_template.jl
index 8b8039e1..4af94ac9 100644
--- a/src/operation/problem_template.jl
+++ b/src/operation/problem_template.jl
@@ -135,11 +135,29 @@ function finalize_template!(template::AbstractProblemTemplate, args...)
     )
 end
 
+"""
+    share_template_references!(template_::AbstractProblemTemplate, template::AbstractProblemTemplate)
+
+Extension point for template types whose build-time copy must share some objects with
+the caller's `template` by reference instead of by `deepcopy` — for instance objects a
+build mutates that callers then inspect on the instance they passed in. The model
+constructors call it on the fresh copy `template_`; the default shares nothing.
+"""
+function share_template_references!(::AbstractProblemTemplate, ::AbstractProblemTemplate)
+    return
+end
+
+function _deepcopy_template(template::AbstractProblemTemplate)
+    template_ = _deepcopy_sharing_network_data(template)
+    share_template_references!(template_, template)
+    return template_
+end
+
 # Deep-copy a template while sharing the network source and derived data by reference:
 # both can hold PNM matrices whose solver caches carry raw factorization handles and
 # deliberately error on deepcopy (PNM #312). Sharing is safe because instantiation
 # replaces the copy's `network_data` outright rather than mutating the original's.
-function _deepcopy_template(template::AbstractProblemTemplate)
+function _deepcopy_sharing_network_data(template::AbstractProblemTemplate)
     network_model = get_network_model(template)
     network_model === nothing && return deepcopy(template)
     source = network_model.network_source
diff --git a/test/InfrastructureOptimizationModelsTests.jl b/test/InfrastructureOptimizationModelsTests.jl
index ad28b334..890cc378 100644
--- a/test/InfrastructureOptimizationModelsTests.jl
+++ b/test/InfrastructureOptimizationModelsTests.jl
@@ -115,6 +115,7 @@ function run_tests()
                     # TODO outputs_by_time.jl
                     # TODO service_model.jl
                     include(joinpath(TEST_DIR, "test_settings.jl"))
+                    include(joinpath(TEST_DIR, "test_problem_template.jl"))
                     # standard_variables_expressions.jl: low complexity
                     # time_series_parameter_types.jl: low complexity
 
diff --git a/test/test_problem_template.jl b/test/test_problem_template.jl
new file mode 100644
index 00000000..b0b98ff2
--- /dev/null
+++ b/test/test_problem_template.jl
@@ -0,0 +1,43 @@
+"""
+Unit tests for the template deep-copy path and its `share_template_references!` hook.
+"""
+
+using Test
+using InfrastructureOptimizationModels
+
+# Minimal templates: one shares a field through the hook, one relies on the default.
+mutable struct SharingTestTemplate <: IOM.AbstractProblemTemplate
+    shared::Vector{Int}
+    cloned::Vector{Int}
+end
+IOM.get_network_model(::SharingTestTemplate) = nothing
+function IOM.share_template_references!(
+    template_::SharingTestTemplate,
+    template::SharingTestTemplate,
+)
+    template_.shared = template.shared
+    return
+end
+
+mutable struct DefaultCopyTestTemplate <: IOM.AbstractProblemTemplate
+    data::Vector{Int}
+end
+IOM.get_network_model(::DefaultCopyTestTemplate) = nothing
+
+@testset "Template deep copy" begin
+    @testset "share_template_references! runs on the copy" begin
+        template = SharingTestTemplate([1], [2])
+        template_ = IOM._deepcopy_template(template)
+        @test template_ !== template
+        @test template_.shared === template.shared
+        @test template_.cloned == template.cloned
+        @test template_.cloned !== template.cloned
+    end
+
+    @testset "default hook shares nothing" begin
+        template = DefaultCopyTestTemplate([1])
+        template_ = IOM._deepcopy_template(template)
+        @test template_.data == template.data
+        @test template_.data !== template.data
+    end
+end