Effects of experience

[CBR]

At longer ranges a breast plate (cuirass) should be able to stop a musket ball. But most shots would hit the horse anyway. In this era armor was not expected to help against missile weapons but was there purely for melee and morale purposes.


CBR

[Sheogorath]

In regards to the musket/club issue...
I really dont see the stock breaking simply because it was used to crush somebodies skull. Unless they were using remarkably crappy wood to produce the muskets of the era, which I doubt they would in most cases, simply because if its fragile enough that hitting somebody with it would break it, then I'd bet that just firing it would also risk breakage.
The model of bayonet would matter as well. If I recall, the British muskets were generally regarded as rather light in comparison to mainland models, besides the French types. Russian muskets were usually very heavy, having been designed with intent to be used as a melee weapon (more on that later).
And, of course, your average new recruit wouldn't care about that, would they? Hence, even IF it was likely that the musket might break if used as a club, they would, if it seemed effective at the time, do so anyway. For instance, if they had a sudden attack of horses and had failed to fix bayonets earlier.

On aiming, it depends on the model of musket. The French musket of the era put the bayonet above and slightly to the left of the barrel. In other words, directly in the line of sight of the person trying to aim it.
And aim does matter quite a bit in the closer ranges (IE: Where you're likely to have fixed bayonets). Having researched the Russian army of this era quite a bit, I can tell you that they were regarded as the worst shots in Europe, capable of firing a volley at sixty paces and missing every single shot. The Russian's recieved almost no marksmanship training, whereas the British got tons of it. Thus, a British unit could easily outshoot a Russian unit. Most likely ANY Russian unit, because the Russian 'light infantry' didn't get much more training than their line counterparts.
The effect on aiming is also subject to the TYPE of bayonet. The British design for the Baker rifle was a 24 inch long sword-type bayonet, which probably weighed quite a bit more than a little metal spike. And I gather that the sword/knife type was more popular with other nations. Of course, it has a great advantage in that you can use it as a sort of axe instead of just a spear, but it'd make firing (and reloading, even if you knew how to avoid it) quite a bit more of a challenge. Some of the early types came quite close to the barrel, which would mean that you'd have to hold your hand in EXACTLY the right position unless you wanted some strange scars on your fingers.

And while a charge of disciplined men might be done in cadence, fresh soldiers are quite a bit more likely to simply run as fast as they can towards the enemy. The Russian army in particular had issues with this, because soldiers were typically overeager to get into melee thanks to the Suvurovian doctrine ('Bullet is an idiot, bayonet is a fine chap', something along those lines). There are accounts of Russian officers having to beat men back into line with the flat of their swords, only to have the section of line they just left try to charge again.


---

All that aside, one other effect of experience I think would be neat would be the unit acquiring 'custom' weapons. I understand it was fairly common practice for veteran units to get their hands on something with better firepower than their standard gun. Rifles, for instance, or models of musket from different countries. I do know that the Moscow Grenadier Regiment was armed mostly with Brown Bess muskets purchased from the British.
Maybe not actually possible, but hey, it'd be neat.