BMP released an Xbox 360 Profile editor. It can do things like change your gamerscore, and maybe more(dosen?t really state what it does). You can possibly get banned from using this. Depending on what you?re doing with it. USE AT YOUR OWN RISK!
Note from NFO: Use at your own risk, anything you modify with your gamertag in this respect will get your Gamerscore reset or get you banned if you get caught. But doing it correctly with this tool you should be fine.