Contracts mode is meant to be an online thing for people to do. You create a contract with some conditions. Then after you save it, random people can play your contract and try to accomplish the goals you set like not being seen or no disguise.
It really wouldn't be fair to use the trainer because you would be setting up a lot of impossible to meet goals in some of the levels.
Why do u advise not to use it?? any reason?? was it online??
Everything from the scores to money is connected to there servers and they have noticed there has been cheating and those peoples scores/money are going to be wiped to zero. No word on them being banned from there game. Yet. So am advising you not to use it on the contracts side.
So take my advice as they have every right to stop you from using the game.