Here in New York if you have a pistol, you have to have a permit for it!
It's ok to have an Encore pistol barrel and an Encore frame, but get a permit for it before you put the two together.
I have talked with the St. Lawrence county clerk about this issue and she said there is no problem with switching from rifle to pistol, etc. Also, with each (pistol) caliber, you must register the barrel and the receiver. So, you can have a bunch of pistol permit amendments, with different calibers and the serial numbers will all be the same!