Fiberglass insulation hole cutter

[metric_taper]

for the least diruption on the insulation it seems a heated cutter would work. Thin edge to melt through. Much caution will be required in use.

Next would be counter rotating blades like a round hair trimmer.

I don't think fiberglass has a low enough melt point, unless your thinking a red heat device that would reflow the glass fibers.

The idea of a nose hair trimmer might work,
Brings tears to my eyes just thinking of using them.