I can't find where to change my nameplate ever since Halo switched to halo.xbox.com. I have looked in Service Record and Stats, but I cannot find it.
Short Answer, you can't do it anymore.
Here is a question made by a user to an engineer on the user interface team.
NOTES: Maybe not a good link but Here is a question in they forum, I don't have access to this area, maybe you have: