Thanks to "Hetelek", "Sh042067", "iTzAdam5X", And "Experiment5X" Over at XboxMB for the tool! I am simply released it to the public.
MW3 Offline Editor
1.Move your Multiplayer Save onto a USB
2.Open Your Save In Horizon
3.Click Content tab then right click mpdata file in there
4.Click extract then save it to somewhere
5.Now open the mpdata you just extracted in the MW3 Offline Editor
6.Now once modded save then go back to horizon
7.Now back to the content tab then replace the file in there with the modded one
8.Now rehash and resign then
9.Put Back into Xbox, Move to HDD and Enjoy!
Make sure your extracting the mpdata file in the con mpdata file with Horizon.
You must have something selected for the Weapons boxes. You need to add the value 0 as None.
Updated When a New Version is Released
Edit: New Version Has Been Released, Just Some Bug Fixes