(make sure you backup all your files first in case you do something wrong)
Step 1: Download the files and go to where you put your game and edit your PRAM.SFO to say 3.40 with PS3SFOEdit.
Step 2: Update the game to 1.02 using the retail update for your region.
Step 3: After your update has finished, open comgenie or ftp and go to:
dev_hdd0/GAME/”Blackops”/PS3_GAME and put the eboot in the pack here
Now if you have the BLES01032 version just use the SFO.PRAM file inc in my pack and place it in that directory overwriting the old one.
If you have another version of the game use PS3SFOEdit to edit your sfo to say 3.40 in advanced edit. SAVE IT then replace it.
Step 5: Double check everything, Then play.
The next part comes from hunter128 from here and seems to only apply if you have run the game previously and been prompted to update.
After you install the pkg launch a FTP server and go to /dev_hdd0/mms/db/ and search a file called metadata_db_hdd open it in a hex editor and search 3.50, and change to 3.41
Big thanks to teh reaper for testing this and confirming it working on external and internal HDD.
Also it seems that multiplayer freezes at the moment, but campaign and zombies works fine!
This is the way that works atm I’m sure there will probably be a simpler way soon.