Plaid Pillagers ask:
Is it legal to have our bumpers able to slide up/down to take them off/put them on using a key hole shaped sliding mechanism?
I doubt it. You are supposed to have a rigid fastener system. I’d ask Q&A, and get busy on an alternate system.
The other thing is, it would be really easy to make you not in compliance with the bumper rule during a match. And I mean really easy (for any arm robot, and quite a few shooters as well). Maybe if you had a lock, but you’d probably extend outside the box. That isn’t good either.
I believe the answer is YES, provided that ALL of the mounting brackets & associated hardware are weighed with the ROBOT and not with the bumpers.
As long as the mounting mechanism is deemed “robust”, you should be fine.
The key is that the bumper weight is just for the bumpers. Everything else is considered part of the robot and must be included in the robot weight.
According to <R08>, the connection must:
STANDARD BUMPERS must be attached to the ROBOT with a bolt-and-fastener system to form a rigid, robust connection to the ROBOT structure (i.e. not attached with Velcro!).
I don’t think that the connection he’s talking about is rigid. It’s like those chains they used to use on hotel doors (just the end). On that ground, it’s illegal. On the robust ground, it may or may not be legal.
Would the mounting brackets and hardware then be counted in the overall volume of the robot as well?
Yes.
Actually, the idea is more along the lines of having a vertical slice in piece of square aluminum stock that the bumpers can slide into, with a method of securing them in place that doesn’t require tightening the bumper bolts themselves. We used something like that today, simply because it was quick and easy to do, and our fenders aren’t finished yet 
And it worked out extremely well for us in our practice matches.
If it’s rigid… However, CD is not the official place to ask. Q&A, on the other hand, is. I’d suggest asking there to make sure. As described, it could go either way. This is one thing that could make bumper design a lot easier next year… if it’s legal.