That's an exception. It's sheer impossible for Napoleonics. Regiments portray a certain era, and do not change their uniform for one specific battle. Because, simple, it would take an entire new uniform which is only useable in THAT battle, which might be a bit too costy. For example, A French soldier of the line should have, to portray 1800-1815, three different shako's, a bicorn, two forage caps, three or even four different uniform jackets, different plates for cartridge boxes, three kind of trousers. Besides the shirts, boots, gaiters, backpack, etc.