The way I do it is make a copy of the project and then add whatever new assemblies there may be to it. You can then update your views that change and leave the ones that don't.
This would be for projects with views. Animations you could do but may be more work than just starting fresh depending on complexity of animation.
If this is a regular situation I would create a smg file that contains just those sub assemblies that are commonly used. You can then simply add then to any project that requires them.