Glad I found it, this was buried under shitload of threads, I used this 3 months agowhen I was modding on halo 3 it work's but this tool don't have the rainbow color option.
You can change it to numbers, OG tag's, and just about to anything.

Download Link from Se7sins

There is a tool that has the rainbow color option in the other thread but for Cod's games only.

This is fun trolling in the lobby, changing your GT name to on of the people in the lobby, everybody gonna be like WTF its two of them lol