I think you will find that several sources speak of the four company French Guard battalions operating in 8 pelotons. As such they would exactly follow the 1791 regulations. You will note that most plates show battalions in 8 pelotons. While line battalions before 1808 were 9 companies, one was a grenadier company. The grenadier companies normally served with the first battalion or were grouped as a higher level reserve.
It is adding a needless complexity to suggest that the Guard had some other approach to drill. No such manual or reference to one has ever been discovered. The members of the Guard came from the line. Guardsmen were sent as cadre to the line. The Guard was intended in part to be an incubator of excellence. Therefore it makes sense that they would use the same manual as tre rest of th army.