Is gluing a piece of polycarb to a limit switch to extend its “arm” legal?
Glue is not permitted for any function other than keeping wires on cortex (Hot glue)
Attaching the polycarb is legal, the glue is not. You would just have to find another way to attach it.
Is electrical tape fine?
Nope. Electrical tape can only be used for securing wiring connections.
Try zip-ties, maybe. Zipties are one of the few electrical management items that can be used on the robot in general.
Last I checked, you are still permitted to bend the little metal arm on the switch. So perhaps you can cut two narrow slots in the polycarbonate and then “weave” the metal arm through the two slots.