I do have an idea, but it's very difficult.
When you open up combat arms, it uses the files that are on your computer to use for ROF, reload time, and the like, it also takes commands from what you do...
Example:
When you have an unlimited ammo hack (that actually works) your sending information to the server saying 2 things
1. I have fired my gun
2. i have used no ammo
When your not using the hack it looks like this
1. I fired my gun
2. i have used ammo
A damage hack would be the same way
legit:
1. I fired my gun
2. that shot will do 40 damage
to make a damage mod/hack we would have to change it to look like this:
1. I fired my gun
2. that shot will do 100 damage
If only we could figure out how... I'm guessing it would be the same as how no spread, no reload, and unlimited ammo would work... then again most unlimited ammo hacks are only visible...