Does the redistribution of costs from outsource to performing in house constitute a change proposal? I believe it is a make/buy decision that does not constitute the need for a change proposal. The contractor has been working with the technical team who have been involved all along and approve the new methodology.
Based upon additional information you provided via separate email, the following response is provided: Your situation does not appear to represent a change in scope. A change at a subcontract level may or may not be a change in scope at the prime contractor level. If the "how" (e.g., make vs. buy) changes but the "what" (the deliverables) does not change, then typically the scope has not changed.
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A useful question to ask is "Have the contract objectives changed?" If the answer is no, then it would be difficult to claim the scope has changed. While I know of no legally binding definition for "contract scope," Cibinic, Nash, and Nagle write "...if the function or nature of the work as changed is generally the same as the work originally called for, the changes will be held to fall within the general scope (Administration of Government Contracts, Fourth Edition, p. 383).