press the trim release and fly the aircraft to a new altitude and then release, the new altitude will then be held.
Not necessarily. In some types, yes, with some autopilot or flight director systems. The original question was general in nature. In other types, one can fly-through autopilot or flight director, but upon releasing, the aircraft will return to whatever the original settings were. In several types of multi-axis autopilot helicopters I've flown (and a couple with force trim but NO autopilot), each had different operating characteristics.
It depends upon the aircraft.