Comp_Mode is the Iffy name for kill. If you make a dongle (the new one), and operate the kill switch, the comp-mode bit is changed.
The significance of the comp_mode bit is not that you can't use it, but that it is the bit that disables your robot in the arena except for a certain 2:00 minute interval.
If you can make use of it, do so. You stilll have to Serin the PBmode byte to tell when the auton_mode bit is alive. Now, about the User_mode bit . . . .