According to the customer service person, you can call Disney dining and they will update the reservation for you. We were asked the ages of our kids nearly every time we checked in at a restaurant, with HDD being the exception. I’m uncomfortable lying, and our 10 year old eats a lot anyway. The person at the check-in desk changed DD10 to an adult in the non-pre-paid restaurants. Some of them were nice about it, and some were rude. shrug