I've been working on modifying the Foundation Library to fit my company's needs, and in doing so, I'm often modifying products and it's subassemblies for one-off products. 

For these one-off products with modified subassemblies, I've just been saving the subassemblies to the product rather than saving them to the library since I don't want the changes to be carried over to all products. However, I'm not sure if this is a great way of going about it, since I recently moved a product with a modified subassembly to another category using database explorer and it somehow reloaded the subassembly from the library so all my modifications were lost. 

Would the best practice would be to save the subassembly to the library under a different name, and use that subassembly in the product instead? This seems like it would be safer for preventing the modified subassembly from being lost, but since the modified subassembly is for a single product, I'm not sure if this is necessary or if there's a better way that I'm unaware of.

How do you all handle saving modified subassemblies for one-off products?