As gas chamber mentioned, on a widebody, 1 pax has little influence on trim.
With other smaller types CRJs for example or when trim critical, then it could make a difference. CRJ captains will often ask for a new loadsheet with any change in Pax figures rather than LMCs.
Looking at a Manual loadsheet for any aircraft type you can work out which zone the change occurs and extrapolate down to see the move in CG.