Does it change the Line Infantry and the Silesian Schützen because they all share the same hat?
There may be a way around it if you remove the hat from the prussianhat brf file and add them in the uniform brf file instead and add a separate hat to each uniform as an extra item(re positioned so it is on the head instead of the floor) and then rig them using the French Cuirassiers helmet rigging so they move with the model.
Never tried this myself with hats, but that is how i get around the pants being shared problem.