The 1808 infantry reorganization brought the change to the battalions' color guards. It had been the battalion sergeant-major and the company fourriers made up the eagle guard. Napoleon changed that to the eagle bearer (porte-aigle) being a lieutenant of proven valor and had either ten years' service or had served in the campaigns of Ulm, Austerlitz, Jena, and Friedland. The second and third porte-aigles were 'soldiers of outstanding bravery' but were illiterate and therefore not eligible for promotion. They ranked as sergeants in their new billets and drew the high pay of sergeant-major.
The matter of the eagles themselves, who rated them, how many would be carried, etc., was not finalized until December 1811 when Napoleon himself actually wrote out what he wanted done.