Pulling fire handles will prevent engine start. Pulling switch arms fire extinguisher; closes fuel shutoff valve; depressurizes engine driven hydraulic pump and shuts off hydraulic fluid supply; trips generator field after a time delay; closes bleed air valve. However all sytems will be restored by pushing fire handles back in again.
Disconnecting CSDs will disable generators and can only be reset on the ground. Engine cowl has to be lifted to gain access to the reset switch. APU generator power will still be available, so a hijacker in the know could still operate the aircraft.
Best way to disable aircraft is to connect a tug and apply the brakes.