You can request to visit a specific restaurant 2 times (on a 4- or 5-night cruise) or 3 times (on a 7-night cruise).
You can request to visit a specific restaurant on Pirate Night or on Formal Night.
You can request to be assigned a specific server (if that server is on the ship).
Those requests work because they would apply no matter what order the restaurants are in and when restaurants repeat in the dining rotations on your particular cruise.
Most specific requests, such as to visit a specific restaurant twice in a row, or the same restaurant on the first and last night, are less likely to be honored because the rotations on your cruise might not allow for them. For example, if the rotation is 1231 or 1233 and you request RAAE, your request can't be granted because no one will have the same restaurant on the 2nd and 3rd night.