You don't have to update to get the MW2 patch, just don't sign in and start up MW2 and it will ask you to download it.
From there you can mod the patch and transfer the modded patch from your 3.41 PS3 to your 3.50 PS3 and host modded lobbies.
The best part is that you can change which patch you want to use at any time!
If you get it up and running, you should invite me into it