You can't. Try modding split screen/single player.
If you meant modding for splits screen/single player (Like infinite ammo,jump hieght,disable AI spawn) use Modio.
Noone has hacked mw3, but I think it is possible to hack or mod modern warfare 3.
There is no wall hacks on Mw3!
yes
You Hack
you dont
Using MW3 Prestige Rank Hack for free by getting it from the Modern Warfare Prestige Hack site and using it to edit and hack your Prestige Level, Rank and unlock everything from guns, camouflage and attachments. Source http://www.mw3prestigehack.net/
With much difficulty.
You can't,and if your thinking about the [Enemy Intel] those are for achievements.
I know I need the Fukien password
Yes, they can hack you from your account. Even if your offline, online, or in a hacked lobby they can still hack you
Keep playing until you get 10th prestige
This is a really simple hack. All it does is doubles your current exp. So, for example if your experience is 2h it will set it to 4h.