I just tried to install a George W. Bush leaderhead, but something went wrong, and somehow I deleted all of the leaders in the game. Now I have to re-install the game, after about 2 hours of work.

Therefore, I assume Sid Meier is a bit of a democrat.

You have just run afoul of Rule One of Modding : NEVER, EVER, work on the default files. Put everything you are doing into a Mod folder.

Only two hours? :)

If you want, I can give you a quick guide how to do it in the simplest way without Modular Loading.