By Daniel Kline Every cruise line tweaks its menus from time to time but Royal Caribbean is testing some very major changes just after Carnival made a big dining change. Taking a cruise — at least for most passengers — means eating a lot. The experience, however, is not all about gluttony, meals (especially dinner) served in the main dining room (MDR) harken back to a time gone by. When you eat dinner in the MDR on a Royal Caribbean (RCL) – Get Free Report or Carnival Cruise Line (CCL) – Get Free Report ship it’s not a quick-serve affair. Passengers may not dress for dinner as they did in da…