I pondered opening my own chokes many years ago. Finally bought Ralph Walkers book "Shotgun Gunsmithing" and read it carefully. I followed his directions to a T.

I always pattern a shotgun to see POA before even starting. After a couple dozen barrels, never had a POI change. A friend and I changed the POI on a 410 by carefully putting more pressure on the choke, in the opposite direction it was shooting. Took a few tries to get it right, cause you cannot put metal back.

Lenard