Really simple, all you have to do is rename BlackOps.exe to BlackOps.exe.bak
Duplicate BlackOps.dat so that you have one called blackops.dat and one called BlackOps - Copy.dat
Rename BlackOps.dat to Blackops.dat.bak and then finally rename BlackOps - Copy.dat to BlackOps.exe (with correct capitalization)
Run the game from the .exe that you have created and run the trainer once at the main menu.