Iv'e found a way to mod gamertag on halo 3. If you already know how to mod you Cod6 Gt then your in luck because it is as simple as signing in both your main account and your modded profile on separate controllers this allows both profiles to view friends, join parties, and play any coop online game with both those accounts. If i get enough questions I will post a youtube tutorial. *Tutorial* 1. Sign in on your modded gamertag with the controller you want to play with (player1) 2. Change the max party size to 1 3. Sign in your main account on another controller or player 2 4. Join your friends games and boast. I recommend not going into matchmaking with an offensive gamertag and sometimes when you do this your gamertag will be blank to other people (Cold blooded pro as someone stated below) Also if you have recon then both those accounts get recon and multiplayer stats are transferred to modded gt  For the period of time you have this modded it will show this gamertag on bungie.net So Don't put in any characters or symbols that cannot be in a normal gamertag. I could not upload a video so I searched through a few youtube videos and found this one. http://www.youtube.com/watch?v=mFOxwpyKnik Credit for Video goes to MythicManiac http://www.youtube.com/user/FrozenMasters *Modding gamertag* 1. Download Ezgt and xtaf (Google) 2. Put your profile on a usb and into your computer 3. Open xtaf and extract your profile (eg. E000000000->FFE000->00000101->E000000000 4. Close xtaf and Load your profile with ezgt and choose the name you want 5. Open xtaf and click inject folder and inject your new folder that was made in the process of modding. 6. Go back on xbox with your new modded gamertag and follow my tutorial above to get it online.