What you could do is just add a new class to the element you want to modify, so for example you have navlink as a class. The class that you’re gonna put on top of that would be navlink 2.
That would be viable, if you could move pages from one site to another. As I work, I often make small but important changes to other aspects of the site as I notice details that need changing, and all those changes would be lost if I reverted to the previous site.
Is there no way to use the Style Manager for this type of thing? (I can’t find any sort of overview of the Style Manager, so I’m not sure yet.)