This is why people who don't know anything shouldn't jailbreak/use CFW. /facepalm
Anyways, once you have the FTP server (blackb0x or PS3 FTP server), open it up, start the FTP service and run FileZilla on your computer. In FileZilla enter the IP that's on your PS3 in the FTP server into the "host" bar. Quickconnect to it, open up devhdd0 -> game -> then open your MW2 region (BLUS30377 or BLES00683 or whatever your region is), click on USRDIR and there's should be a bunch of files with "patch_mp.ff" at the bottom. Download a modded patch such as DEREKTROTTER's Mossy v8 edit and drag it into the FileZilla folder. It'll ask to rewrite, click yes. Go back to your PS3, exit the FTP server. Hold the PS button, turn off system. Restart it and load MW2.
If you have done everything right you should have a patch on your PS3. Enjoy!