compressed air method to change seals

Pressure is pressure regardless of volume so not being at TDC should be fine. As mentioned, being at TDC just adds a safety factor that the valve does not drop. I use the rope method, due to the fact that sometimes you have to tap the retainers pretty hard to break the keepers looses, and no way the valve is not going to move when you do.

I dunno what harm it does if the crank moves..... there is no propeller attached to it.