Reloader7RM,
Don't know what you mean by "chamfering" in this instance, but yes, POI of a pattern can be changed by filing one side of a fixed choke.I have done it myself, but it normally means the patterns will open up as well.
A Foredom tool with a sanding drum works much better than a file. It can work quite well, especially if you'd like to open the choke anyway.
