[andy]

Hmmmm.....
Our team tried this last year, we had a set of pedals that acted like "brakes"
The way they worked was they overrided every signal and applied electronic brakes. That way, if we needed to stop, even if the joysticks were pushed all the way down, we could hit the brakes and the robot would come to a stop.
I built a relay box, that had four SPDT relays in it that were controlled simultaneously by a SPIKE.
As far a leagality is concerned... We asked the Q&A and got an ambiguous answer... I will see if I can find the exact response. If time permits we plan on doing the same this year. But instead of four realays we have one 4PDT relay we will use.

Good luck!
-Andy