Instructions
Connect your memory card to your computer using a Data Migration Kit. Open Xport 360 and run as administrator.
Click "File," "Open Memory Card" and then select your memory card.
Click on "Partition 3," "Content," your gamertag ID and then a code will appear from the drop-down menu. This is your profile number. Drag and drop the profile number to your desktop.
Open EzGt. Click on the file menu and select "Open." Highlight the file you extracted from USB Explorer and double-click on the file. Your gamertag name will appear in the dialog box.
Delete the gamertag name and modify it to your preference. For instance, you can change your gamertag ID to "Halo Man." Click on the "Options" tab to number the "Modded Profile Number." Select a number to save the profile and click "Save."
Open Xport 360 again. Select "File," "Open Memory Card" and select your device and click "OK." Navigate to "Partition 3," "Content" and drag the file you saved from Step 5 into this folder. Eject your memory card.
Plug the memory card into your Xbox 360. Sign in using your current Xbox Live gamertag. Go to "My Xbox" and select your gamertag. Select "Change GamerTag" and navigate to the gamertag on your memory card.