I'm surprised that Disney would bump ADRs like that, but I suppose they would rather call you and switch your res than not be able to accommodate you when you show up. Weird.
Anyway, I worked at the Coral Reef up until the end of October and the lunch menu varies only very slightly from the dinner menu. There are no sandwiches, save for the open faced barbecue salmon "sandwich" and the lobster salad "sandwich", but they are not typical sandwiches. Coral Reef is considered fine dining, so the presentation is much different than what you'd expect.
As well as those "sandwiches", much of the dinner menu is served at lunch in smaller portions for smaller prices, like Grilled Mahi, Blackened Catfish, NY Strip Steak, Prime Rib, and Grilled Chicken. There are only a handful of dinner entrees that aren't on the lunch menu. But unfortunately you won't be able to order them at lunchtime.
If I remember correctly, the appetizers are mostly the same for lunch and dinner (order the creamy lobster soup. it's a do-not-miss in my opinion) and the desserts are the same at lunch as at dinner.
I hope this helps.
Callie