I got that little fuelpump switch.

My question is:

Is it bad for the engine if you turn off the engine not by removing the key, but by cutting the power to the fuelpump?

I got a 12A BTW

 

on a 4 stroke car, no, it wont hurt anything really except when it gasps for fuel at the end it could cause undue stress on the internals (not enough to really worry about though)

On a 2 stroke however, it will cause a lean condition which will ultimately shred your motor.

 

eeeeeeeehhhhhhh ok.........let's talk rotary here

 

the rotary motor is essentially a 4 stroke motor. separate strokes/rotor sweeps for intake and exhaust passes.

Well, ok, its more 4 stroke than 2 stroke, so follow what I said for the 4 stroke motors. It will be fine.