Depending on what it is I may be able to help. There are certain things you can do that can be considered "Mods".
Gamesaves- You could download, and or edit a MW2 Gamesave using Modio, or just download one using a gamesave hosting site. You of course would have to rehash, and resign the gamesave so your profile can use it which can also be done with Modio. This type of Moding will allow you to have "God" powers in Campaign, and Special Ops offline, and online. (Although with Special Ops your teammate (If your playing online.) Won't have these powers. Another thing you could do is use a program called EzGT, to edit what your Gamertag is/looks like in the pre-game lobbies. You may edit it to contain buttons, colored letters, and even change it to already taken Gamertag. However, if someone takes a look at your Profile your original Gamertag will show. This can only be used in COD:MW2. (That I know of.)
ISO Editing- This is for people with JTAG'd XBOX 360s, that have Retail consoles as well. You would have to have the extracted ISO contents of MW2 on your JTAG's Hard Drive, and a legit or burned copy of MW2 for the retail version. After patching the MW2's default_mp in the extracted contents on your JTAG, with a patcher. (Can't remember the name of it.) You can search the web for Infection patch.mff files that you put in the directory of the extracted MW2 contents. Then while both consoles are hooked up, you go to System Link and have your JTAG host. Have your Retail console join, and follow the directions that came with the patch.mff. (They differ as to what button combination is needed to activate the Infection Mods.) After you follow those directions you'll have whatever powers the infection gave you. Yes, they even work online.
NOTE: (Infections mods are like zombies. Imagine the JTAG is a zombie that infects a retail console, that retail console now has the same attributes of the JTAG while on MW2. If the XBOX is turned off the Infection will go away. However I believe in the latest Title Update they patch the ability to be infected, and go online. So either you wait for a patch, or no one is bothered to find a loophole.)
EXTRA: Since, you don't seem like to have a JTAG'd XBOX 360, you'll have to use the gamesave mods. I'd recommend Modio, because it has a nice method of downloading saves from it's repository, and also rehashing, and resigning them to a profile.