This is what you have to do:
Start the ID Changer.
Start OFP.
Alt+Tab, enter ID, back to OFP.
Press F6. Fake ID is now active.
Connect to a server. When you are connected, press F7. The server now thinks you never changed your ID.
Cheat, leave the game. Find a new server.
Press F6 to activate the fake ID again, connect, press F7.
The fake ID only has to active while you are connectiong to the server.