Ohminnie...I have no idea how to request a dining rotation. Our first two cruises were on the Wonder, and we took what they gave us. Had no idea that I could change them. Although, I had read what you might expect.
We had (both times) PTA. The kids were younger than I had thought for that rotation, but I guess since we were late dining, that's where they put us.
For this cruise, so far, it doesn't seem to matter what the rotation is, because we don't know which nights are which.
For the Mexican Riviera, which we are assuming is the same as any other 7-night, I am going to try to request (through my TA) APLAPLA....it would fit right in with the "formal" nights.