If you mean during the
ABD tour, there are no Disney characters--there may be an actor or two playing a role (such as Marco Polo in Venice), but that's it. You get the Disney attention to detail, but for characters you gotta go to the Disney parks or ships! As to adding on, we have done that later in the trip without problem--BUT, we always book our own airfare and made those decisions before locking in the flights. I can't say if you would be able to change things if you booked flights via Disney already.