A quality gunsmith that knows his/her stuff that has machine shop equipment can do this task.Who is good at jug choking,always wanted to send my NE 12 ga. out to get it done.
They should be close enough that you can oversee the job and verify they can do the job without making a mess of your barrel.
If you don't have the information available to you, message me and <i will walk you through it.
It is not complicated with a single barrel, but much more so with a double.
Fred