I was recently at a national park, and miscalculated the last minute changes in who was carpooling with whom. We ended up with the regulation 6 people, but 3 cars (the limit is two). I think this is more disruptive than an extra human!
I fessed up to the ranger at chcckin, and she said it was no problem, just come to the booth in the morning when the third car arrived and they would give us another car tag. We did that, but on duty in the morning was a camp host who was more strict. After much discussion, he had us unpack one car and move it to another lot.
Moral of the story: They will not kick you out. They might give you some minor grief, but I think park people are all about wanting everyone to enjoy the park.
