Oh I'd never bar people from the GTW jobs, or any other aspect of the game. If it's legal in the game (not using 3rd party MODs) then it should be legal in the ISBI challenge.
Also, always always ALWAAAAAYS play however you need to in order to have fun. I didn't pose the question here in an attempt to try and rules-lawyer you. I apologize PROFUSELY if that's how it was taken. I just happened to think of it while I was posting my comment and it attached itself.
I've always been a firm believer in enjoying your game however you need to (that's the whole reason of playing, right?) so if you decide you want to change something in the rules for your game then you go right ahead. :P