You saved your game didn't you? You never save when you use cheats. I never do. That way I never have to worry about that. Sorry I don't know about undoing that.
if it didnt workj taking it offf, itws cause you missed the code plain and simple..i use it..fly over to the airport with the tank..land and take it off..drivenormal..make sure ya hit the code the 2nd time.peace