Hi Phil,
Thank you for you question in the Community.
I don't know of any way to do this. The data is very different between Production and Assembly, not to mention WIP exists in Production, but not in Assembly.
You'd have to almost reverse out what was done for non-finished Production Orders....such as consumption and output reversals. Then recreate them via Assembly. With Finished Prod. Orders, if you are possibly inquiring on those also, there really is no way besides data manipulation in the backend.
Sorry I don't have a better answer, I have not heard of this request in all my years, so it is probably not something in the scope of Development.
If you are a customer and have a Partner, I'd recommend inquiring with them and perhaps they can do something more if they know more about the specific scenario.
Thank you,
Bryan