You can change the Windows Live ID of an account on the xbox.
While signed in, if you press the big X, then go to the system blade, and down to account management, in there will be an option called Windows Live ID. That'll let you change the windows Live ID of the account you're currently signed into.
Just change the Windows Live ID of your other account that's on Bungie.net to something else, then change the Windows Live ID of your GR4Mz7 to the one on Bungie.net.
Simple
great worked. thanks