Power changes and trim forces. related to position of Center of Mass (CoG), or Center of Pressure? Theoretically (and Actually) do power increases cause a pitching tendency (and a need to adjust pitch trim), because the thrust line is not aligned with the Center of pressure, or, as I understand it, because the thrust line is not aligned with the center of mass (CG)?
I was recently told that the Cessna 182 is particularly sensitive to abrupt power changes in the landing phase (at slow airspeed) because it is a high wing aircraft, and the thrust line is below the Center of Pressure. i.e., Increases in Power generate a pitch up moment, requiring down trim to compensate, and reductions in power generate a pitch down moment, requiring nose up trim to compensate.
This strikes me as wrong, I believe it the alignment of the thrust vector with the center of mass of the aircraft, (the Center of Gravity (CG) as it is called), that determines the moment generated by thrust vector.
Your intuition is correct.  Each of the three principle axes of the aircraft originate at the center of gravity.  Therefore, all rotation in either pitch, roll, or yaw occur around the CG.
The center of pressure is a place along the chord where the lifting force acts on the wing.  It is not a pivot point like the CG is.  In fact, an increase or decrease of lift will actually produce a pitching moment around the CG if they are not co-located along the longitudinal axis.  This contributes to the relative stability (or instability) of an aircraft.