[45Auto]

I have NEVER seen a robot that had the edge of it's bumpers modified to clear a mechanism pass inspection.

R21 has traditionally been interpreted to allow minor clearance pockets on the rear face (frame side) of the bumper for bolt heads, E-clips, etc, that protrude less than 1/4" past the frame perimeter.

If I were you, I would modify the robot to use un-modified bumpers NOW while you have time and tools available, rather than have to do it in the pits at the competition.