If you want to avoid full drain ,once youll open the thermostat lift up the pipe ,and will flow some fluid ( you cant avoid it) something like litre(more or less ,get 2 ltres spare) just top up it once you done( try not to mix different fluids)
And as i recommended you should put something above the electric ( under thermostat) because of the fluid .
Edit:
I saw what you asked ,you should NEVER do it!! Youll get overheat before youll turn off the engine .