Demonic, don't forget to update your GamerTag associated with your XG Profile & request a new Username via the Help Desk.
To update your "GamerTag", click "About Me" on your profile (directly above), click the yellow pencil next to "GamerTag", update it, then "Save".
To request a new Username / Login Name, click "Help Desk" in the top right corner, click "Request Login Name Change", type your new GamerTag, then click "Request New Username".