As far as I know, NO. If it was purchased as a pistol, it can be converted back and forth. But if it was bought as a rifle, it must stay that way. I've never actually called and asked one of the lead officers at the BATF(E).
So you might want to do so.
That brings up a really important comment. Anytime you have a question for the BATF(E), you need to do two things when they provide the answer. #1 ask them for the exact regulation number that pertains to that question.
#2 if they hesitate for a few seconds (most of the time they will) ask to speak with the lead officer, and pose the question to him/her. Again, ask for the specific regulation number so you can look it up.
You need to look up the regs and balance it with what you are told. Many times people at the BATF(E) will answer a question offhand, and really not have a clue as to what the real regs are. And/or the regs are left open to interpretation and it will depend on the officer that reads it to decide if you are in violation or not. If your question falls in this category, request a full written reply, signed, from a Special Agent In Charge, stating what they have told you.
I assure you, saying "Agent so-in-so said..." will not help you one bit in court, or in front of the magistrate.
Didn't mean to make this so long.