Do you think it would be possible to let regiments create their own uniforms for their ingame unit? Stick a crapload of different and historically accurate coats, belts, pants, hats, etc. etc. into a unit editor, and each clan-regiment will be able to make a unique uniform for their ingame unit that they could display and show off on the "Regiments" tab. This would make the clan system even more personalized and intimate, as you won't look anything like the other hundreds of clans in the game. People could look at you and say, "Oh! He has those large silver buckles on the grey belt! He's from the 57th New Jersey!" or something of the like.
EDIT: Each clan could make their uniforms as historically accurate as they want, or make a completely custom look, but as every single uniform piece is historically accurate, they won't look too ridiculous.