I think Craiggo managed to make several of the characters who couldn't use the musket, use them. But I don't know if this made it into GoF! or not. Part of the reason why adding the musket as a usable weapon in the game not making it into the mods sooner was certain bugs with the interface and the gameplay issue which Darth brings up. But for sure there are
some characters that have this ability which may or not be enabled in GoF! Off the top of my head, all the Blood models have this ability, this includes Peter Blood, the Spanish Inquistor guy, one of the French characters and maybe one more which I can't remember.
Ideally, if I understand you correctly, you want to create a toggle which would switch the animation from the standard melee version to the musket and back again. Similiar to when you put a new curiass or clothing, although this is a change in the model, not the animation, these characters still use the melee animation. Another thing to consider is, there might be a game limit on how many "toggle's" the game allows, I haven't tested this out though. Currently the game allows eight? versions of a character model in the hero descrbribe, one is the default, three are clothing options and the rest are the curiass varients but only one entry for the character animation.
But if you can find away, or at least make some kind of headway into the subject, by all means, update the thread
A long time ago I was considering making a musket exclusive character for the CM, I even had the character ready and a backstory but this idea never came into fruition was put aside. Plus I think there was an infinite ammo problem

Kind of takes the fun out of things if you know you'll never run out of ammo.
@Darth
Well, that is the draw back of the musket and it makes sense since a man with a 42" or 48" long musket wouldn't be swinging a sword and reloading at the same time.

Generally, during this time, musketeers and the ordinary rank and file soldier were two seperate people. Soldiers in the front with swords, etc and musketeers in the rear.
I envision playing with the musket such as that the player stands behind while his officers dispatch the soldiers. This though does make for more challenging game play, especially in boarding actions where if you find yourself alone or fighting the enemy captain, the musket melee is a poor substitute for a sword.