Section 58 (2) of the Firearms Act "nothing in this Act relating to firearms shall apply to an antique firearm which is sold, transferred, purchased, acquired or possessed as a curiosity or ornament."
So very definitely yes. So long as your original antique muzzleloader is kept solely as a curiosity or ornament, then it may be kept or sold as an antique.
The best approach is to write to your firearms licensing department and tell them that you are not using the gun and that in future it will be kept as an antique. That's it. You don't need them to do anything.