If you were to SBR an Encore could you change to a short shotgun barrel without another tax stamp?

I know it's ok to change calibers but...

I have never seen anything official from BATFE, but was told by an 07/02 that if it was a smoothbore barrel it would need to be registered as a sbs.

If it was a rifled barrel (even as a shotgun gauge chambering) it would be a sbr.

There are a few scenarios I have thought of in this respect. The TC is one of them, others are cutting down a long gun with both a shotgun and rifle barrel (the old 22 mag/ 20 gauge O/U), as well as cutting down a rifled slug gun.

I have never pursued it beyond a discussion stage