modify cots

would we be able to drill holes in the extruded rectangle on the super shifter gearboxes to mount the gearbox to the chassis without violating the rules?

It turns COTS into FABRICATED ITEM. That’s all it does rules-wise.

In other words, yes, you can modify COTS items as needed for your application (with a few limitations, such as pneumatics per <R67> B). Specifically, there is nothing in the rules that would prevent you from modifying gear boxes.

The only point you may want to consider is reuse of those gearboxes in future years. The rules (specifically <R29> this year) very clearly state that COTS items that have been modified for previous years robots cannot be used on this year’s robot, and it’s a pretty safe bet there will be a similar, if not identical, rule next year. In fact, the example they give is mounting holes like you describe!

So, if you need to drill mounting holes, go for it. There’s nothing preventing you from doing that. However, keep in mind that it will prevent you from using those gearboxes on a future FIRST robot.