You can't race in a restricted class, refuse to have your engine torn down and then expect everyone to believe your legal.
If UMP doesn't enforce this they might as well throw the rules out the window.
I do agree with your first statement, though no one can prove it to be legal or illegal so we are speculating. If the UMP rules do state you can refuse a claim once before fines and suspension then they followed that. So the problem isn't rule enforcement but the rules themselves.