A few British regiments which played famous roles throughout the Napoleonic War which I would love to see added:
2nd Dragoon Guards (Scots Greys)
88th Foot Regiment (Connaught Rangers)
1st Foot Guards (Grenadier Guards)
Last but not least; 92nd Highlanders (Gordon Highlanders)
Also, swords need a buff. They are completely useless against bayonets. With a sword you need 4-5 blows before you can kill an enemy, bayonets only require one blow and it has greater reach than a sword. Musicians and officers need to be able to better defend themselves. Also colour bearers should be able to melee while holding the flag.