There is no "switch" per se; the switching is done when contact is made between the bulb assembly and a lip inside the top end of the tube, under pressure from the battery spring. If by switch you mean the bulb assembly, you just push on it (with batteries out) until it snaps out of the retainer and drops through.
It didn't hurt anything when I did it. Yes, it can be reassembled.There is no bulb, but will pushing the LED/switch assembly out damage anything? Can it be reassembled later?