isn't the user mode controlled THROUGH the competition port, which is completely covered by the competition "teather" (i don't know what it's called, but it provides power, so i'll call it a teather
). unless you cut that open, and touch a few leads together, you can't alter the user_mode bit, cause it's part of the PB_mode byte, which is controlled by the referees. so, that leaves you without a bit to control what's going on in your robot...
there is a way around this though, but it's highly unethical. i'm pretty sure it was posted here before, but well, here it is again. another bit in the PB_mode byte is the competition bit, the one which disables you. you can disable yourself through the E-Stop button. so, you could technically use that to control your robot in the way mentioned above. as i said though, it's highly unethical, and almost sure to get you a nice DQ. to eliminate this, FIRST should make the E-Stop button work only once during autonomous mode. say your robot goes wild, you hit the E-Stop button, robot is disabled till the end of the 15 seconds. this would stop this idea from being used. on the other hand, i'm sure if teams use this, the referees would get mad. but, then again, there's no rule against it, yet.