This is a way: https://www.mpgh.net/forum/showthread.php?t=820452
You can take some weapon codes in this thread and edit your Totalitem, for example if I wanna change SSG82 to Barret Cammo I just need change 13 to 58.
SSG82 in array of byte:
If edited in Cheat engine will show 2 identical memory region, so, edit the last.Code:C2 00 00 00 02 00 00 00 33 02 00 00 53 53 47 38 32 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 01 00 00 00 13 00 00 00 01 00 00 00 00 00 00 00 00 FF 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 30