Hey TTG, this post will give you a simple way to mod Spec-Ops online with a friend.
[Its a very simple savegame.]

Tutorial:
1)Open a device explorer of your choice.
2)Find your profile, then find your Mw2 savegame (savegame.svg)
3)Replace your savegame.svg, with this ---> [ Register or Signin to view external links. ]
4)Start Mw2 and RESUME campaign.
5)After it starts, give it a few seconds, then SAVE and QUIT.
6)Go to Spec-Ops and start Two Player Online.
7)When it prompts you to choose a map, simply hit B.
8)Once in the checkerboard lobby, invite your friend and start the game.
9) Beat the mission using mods. To activate mods, press Back.
10)Once activated, the controls are: UpDpad=NoClip, RB=NoTarget, LB=Slo Mo, LeftDpad=Default Weapon, Down Dpad=Drop Guns. Infinite ammo is automaticlly given upon activating mods.
11)After completing the mission, you can play any mission you like.

Remember to activate the mods at the start of every new mission.

-Hordichuk