Your most likely correct in that the TC can change barrels giving it centerfire firearm potential. Never thought of that.

The TC Pro-Hunter is an Encore. Muzzleloader Encores are switch barrel rifles. They are treated like centerfire rifles by the ATF.

Pure muzzleloaders that cannot be made into a shotgun or centerfire rifle with a barrel change are not classified as firearms. You do not have to fill out the paperwork and they can be shipped USPS, or UPS without any special requirements. As mentioned there are a few states that have more strict requirements that also include muzzleloaders. The ones I can think of immediately that I think have special rules are New Jersey and Illinois. Arizona is not one of them. Probably California might be another since they have pretty strict requirements for most guns of any type. By the way taking a real "firearm" apart does not get you out of the requirements. The action or frame that carries the serial number is the item that cannot be shipped without going through a FFL holder. As you might notice a lot of the muzzleloaders do not even have a serial number. It helps when shipping a pure muzzleloader to not specify that it is a gun. If you must specify something make sure to call it a muzzleloader and be sure to emphasize that it is not a "firearm". My USPS does not even ask and I have shipped three in the last couple of years, and received two the same way.