I had read somewhere that Hunter Arms would bore the chokes to what ever you wanted. They asked how many pellets in a 30" circle at the yardage you specified. They would ask what type of shell you were using, size of shot and drams of powder.
I hear of too many people buying a new/old gun that they haven't shot yet and want to know who can open the chokes. I would bet five different shell manufacturers offering the same load and you would get five different patterns at the same yardage.
My opinion to them would be, leave it as it is and learn to shoot with it.