I would suggest to just let it go and see what you get. We joke amongst ourselves before going to the 1st MDR night saying "are you ready for the MDR roulette?" - and 6 out of 7 cruises we've been fortunate to have had good table mates.
After all, it's only 60-90 minutes a night (if that) you spend with other people at the same table. It's no big deal IMO.
Also, may I ask you, about your request for main dining:
- How far away is your cruise? and is it a 7 night or less?
We've also requested a change for our upcoming 7 night and nothing yet. We sail in 3 weeks.