As You have stated as well as others, there are many variables, but I would prefer to cut It off, drill It out, then bore, or chase the threads out if threaded.
I change out a lot of ferrules by heating them up, and simply twisting or pulling them off the tenon, but in general most of them are not being saved anyhow, so I have a small butane torch that I can set on the lowest setting, and It heats them up enough that they come off the tenon in a fairly clean manner. That's fine and works well for me when installing new ferrule material, but even on It's lowest setting the torch still scorches the old ferrule.
Another trick is to use a piece of leather to heat the ferrule up, This may do far less damage to the ferrule, but from My experiences is far less effective at heating the glue up as much, but depending on how well the old ferrule is on there, and the type of glue used, It's possible if someone was patient enough, that It could be removed that way, although My preference would still be cutting the ferrule off, and re-machining the inside.
Just hope that the ferrule is centered well with the tenon, or unfortunately You may be cutting the shaft up for no good reason. With that thought in mind Maybe I would at least give It a good shot of getting the ferrule off clean, before attempting to cut It off. It could end up being pretty tuff to do, but If It was to come off clean, so that You can look at the centering, and It was off too much to be used on a new shaft, then It could still be re-installed on the old one again. Good Luck with It
