Ok do this:
1. On your 3.55 go to game data utility and delete the mw2 data.
2. Start mw2. When it asks you to update to 1.12 say yes. Let it install.
3. Use FTP or Filemanager and navigate to dev_hdd0/game/BLUS30377/USRDIR. Delete the default_mp.self. Overwrite patch_mp.ff with your modded patch (it MUST be named patch_mp.ff).
4. Exit filemanager, boot mw2. Your mods should be working and you're ready to data transfer