The first time i shot a muzzleloader was back in the 40" s,I have used oil,homemade lard,crisco,bore butter (probably crisco with a little food coloring).I would think that if you used anything to coat the barrel after shooting and shoot the rifle afterwards you are seasoning the barrel to some extent.
If T/C didn' t think much of the idea,I don' t see why they would put in their manual,telling you how to do it and how to clean it
T/C quote: The #13 bore cleaner will remove only the surface coating of natural lube not the lube which has impregnated the pores of the steel.
I would say do whatever you think works for you.