There isn't much difference between the 2nd Short Land Pattern Brown Bess of the AWI and the Napoleonic 3rd India Pattern Brown Bess, and likely not that much visibly at this scale. Main visual difference is a slightly shorter length.
Your biggest issues using Napoleonic arms would be two things:
1. Uniform: the lace on the cuffs is all grouped together on the Napoleonic era tunic, while the RevWar coats have the cuff buttons and lace equidistant around the whole cuff
2. Manual of arms. The poses presented in the Napoleonic Line Infantry box are based on the manual exercise of the time, which changes drastically from the previous version (1764), most notably in fixing bayonets on the ground instead of holding the musket by the swell in the left hand, so I would avoid using these arms. Likewise anyone loading/ramming with the butt of the musket on the ground is inappropriate for AWI period.
Otherwise they should be interchangable...
[note: oops. Already posted this before, and in the same thread.
Feel free to remove]