I changed the POI on an old Darne that came with XF/XF chokes. I wish I had taken notes at that time because I moved the POI where I wanted it and opened the chokes to IC/M.
I think one can calculate how much to remove from what side of the barrel by measuring the diameter of the final theoretical pattern so that the POA coincides with the POI and figuring out the constriction difference in thousanths and removing that much from where need be. Something like that.