That all depends on the DM. They could rule that you charm the target, not the non-existent person, and therefore you don't gain the benefits while disguised.I like to combine 'friends' or 'charm person' with 'disguise self' or use of a disguise kit. Target will get angry, but at a non-existent persona.
Yeah, that was my thought as well. 5e charm person is, as others have said, pretty much worthless without the DM overtly contradicting the rules text or introducing a house-rule like the above "Wis save to realize what happened now instead of in two days" or the like.Is this for 5e? If so all of these suggestions are for naught. The victim knows who cast the spell on him.

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.