The throttle should not stop working, that doesn’t sound normal.
If you want the aircraft to start on the runway (this is not related to use of the Bravo throttle quadrant), select an airport or runway directly in the world map instead of selecting a gate or parking ramp. It will start with the engine running.
There is no way to change liveries once on the runway (unless perhaps there’s a developer mode way, in which case you should search for developer mode).