Since the objective is to get the prop to turn and windmill,it would be prudent to leave the magnetos `off`,to prevent an overspeed if diving,then turn back `on` after recovery. I would have thought that ,with the throttle closed,there would be minimal airflow into the cylinders,but at speed,if the throttle is quickly opened,there maybe sufficient`push` on a piston to turn the engine..`.However,I expect `DAR` may like to subject his 152 to some definitive restart trials...!!
Slight thread drift..I used to teach student t-ps and ftes at a civlian t-p school,at the spinning phase in a CAP-10 ,that we would initially do a couple of spins,in both directions,with the prop stopped.this should demonstrate the true spin characteristics of the aircraft.This was then followed by spins with the engine at idle,where one could see that most prop-engined aircraft have different spin characteristics due to engine power and prop rotation...
Perhaps DAR could try this ,feathering a PT-6 on a `Caravan....?