Changing preferred copy in Steam; moving mods to new path

[ElMagit0]

Hi, I've been playing Skyrim via a friend's game with the steam library sharing and want to buy the game for myself. 
How could I move all the mods to it without having to install them one by one?

[Pickysaurus]

If it's already on your PC, just switching to your Steam account and buying the game shouldn't change the installed files?