Customizing interface.

Well I wanted to customize a interface , I've download a already edited one from there , but now I got a few problems , it has 426 files ! Do I need to edit 1 per one? What should I pay attention while customizing it ?

Thanks for your time^^
Cheers

Your questions are redundant. Let me state the obvious. Of course you need to edit them one by one, they don't magically edit themselves after you edit just one of them.

I dont know , sometimes there miracle functions or programs that allow's us to change diferent things at same time.
Thanks :3