Unless I'm missing something, it sounds like what you're looking for is a version control system.
This would allow you to keep backups of all your files, and you could revert back to earlier versions if you make a change that makes your site blow up or something.
You could also just try "right-click" -> "copy" -> and paste, giving it a new name. Sort of a crude, home-grown versioning. SVN is probably a good place for you to start, but there's also git and mercurial (either of which might be a bit much for someone with simple needs).
Is this what you were getting at, or have I just completely missed your point, here?