thanks to godzcheater from xmb
its the same thing as halo reach, so here is how to edit credits from reach, but instead of looking for the number of credits, youre looking for your OVERALL xp
so for me i was sr-3, and it says 585/980xp
but since i already did ranks 1 and 2, its 2165 overall, which is what you need to look for
here's how to mod reach credits, which is the same way to mod halo 4 xp
http://www.youtube.com/watch?v=WNIRY7vceZA