I would say at least ask the wait staff whether you can order the lunch appetizer during dinner. They worst thing they can say is "no."
My only experience with ordering "off the menu" has been at Olivia's - after they took conch fritters off the restaurant menu and just had them at the walk-up bar outside. They always allowed me to order them.
I will say, in their defense if they deny your request, that the kitchen may simply not be able to accommodate a request for a dish that they don't serve during dinner time. It may be one thing to modify a dish to deal with food allergies/special dietary needs, but another to pull out an item that isn't on the line, so to speak, during that meal.
