nipping the 2 pins is fine, just be sure you aren't damaging the actual connecting metal pins, only the plastic bits

It depends on what you do with the switches, after clipping them.

Clipping 5-pin switches down to 3-pin doesn't create any problems, unless you want to later use those switches in a plateless build.
If you're doing a plateless build, the extra two pins will help keep the switches aligned properly, which is normally handled by the plate, when using 3-pin switches.
I've seen some really horrible looking plateless builds, where the keys are all just aligned haphazardly to each other.

It's ok to remove extra 2 pins if your PCB doesn't support that

Okie dokie, thanks!

Yup, got it. Just the 2 little plastic ones next to the center post. Thanks!

Thanks for the clarification. These switches are a complete assortment of switches, no duplicates. Once I find the ones I want, I'll buy a fresh batch and these will stay as testers/fidget gadget.