The rosettes are actually the usual cockades in the traditional blue centre/red/white outer concentric circles used throughout the French Napoleonic army. As far as I know, the Marins de la Garde were the only unit to wear them on the side of their shakos as opposed to the front, which was the general rule (units wearing helmets or bearskins had them on the side too, of course). However, I can only recall them being worn on the left side of the shako, I can't remember ever seeing an illustration with them on both sides. Am prepared to be educated further on this point, of course.
I have looked quickly at this today and can only find rosette on left but like Richard very happy to be educated ...
Perhaps Stu or Carl might share any references ......it's always good to learn
Happy benchtime
Nap