Perhaps the steps might be of interest, as initially in 1806 it was one regiment was of two battalions:
Fusiliers of the Guard - 1 battalion from the grenadiers; later to become the Fusilier-Grenadiers with 2 battalions)
Fusiliers of the Guard - 1 battalion from the chasseurs; later to become the Fusilier-Chasseurs with 2 battalions)
Napoleon created the Fusiliers of the Guard on 19 September 1806 (as the Imperial Guard moved toward Prussia). He converted (and eliminated) the former vélite-chasseur battalions. Previously on campaign, Napoleon assigned two companies of the vélite battalions to each serve with each battalion of grenadiers and chasseurs. Thus, although part of the brigade of grenadiers or chasseurs à pied, they did not march as separate units.
A decree dated 15 December 1806 created the Middle Guard, separate from the Old Guard, and established the from the Fusiliers of the Guard two regiments, one each of fusiliers-grenadiers and of fusiliers-chasseurs. This occurred as the infantry of the Imperial Guard moved from Berlin toward Poland and it converted and eliminated the former vélite-grenadier and vélite-chasseur battalions.