"As for cooling to stabilize temps for shutdown - it is the cooling air supplied by the compressor that cools and stabilizes the internal engine component temperatures - a PT6 gas generator can't tell if the prop is in feather or beta - increase the engine power though and watch the ITT rise. Do keep an eye on the oil temp. BTW feathering has no significant effect on fuel flow in a PT6 - they are a free turbine."
I agree the engine internals are cooled BUT depending on the aircraft type, you have to be careful where all of that hot exhaust is blasting on to(Caravans; would be the side of the airframe, king airs; nacelles etc.). I think that that was what the original cooling comment was directed at. My 2 pence.
Otherwise, I think it's pretty silly to invent your own procedures, as per previous comments. Is this in the 'Normal Procedures' section of the manual? Of course, floatplanes are the exception...