A reset tool will not set the airbag off. It's purpose is to clear the error codes logged in the memory of the airbag control unit, which is what brings the light on. The light goes out when the errors are cleared. So no worries there.
However, if moving the seat is known to bring the light on, then the likelihood is that you have the usual dodgy connections under the seat. There is/was a replacement wiring loom that corrects this, and I have had it fitted to my car, but as I didn't fit it myself, I don't actually know what they changed on it, but my suspicion is that it will use different connectors. All it takes is a momentary break in the circuit and this will bring the airbag light on, and it will stay on until the error code is cleared. Whilst the light is on, you will have no airbag(s) or seatbelt pre-tensioners.
If it were me, I think I would prefer to actual fix the problem, then I wouldn't need a reset tool.
Arctic Silver '99 Z3 1.9 & Black '59 Frogeye 1275cc