It's exactly like refactoring. You can replace a component that does something with a different structure for accomplishing that. Of course, if the system was t

It's exactly like refactoring. You can replace a component that does something with a different structure for accomplishing that. Of course, if the system was tangled, then you may need to refactor other components first (read: relocate them to give room). The structure of the base around something is going to place limits on the refactoring. If the base is so horrible that you decide to gut it entirely, it's just like a rewrite.