This is interesting. I guess a lot of passengers have requested this, for =X= to make the change. I hope it works well for all.
We just booked our Panama cruise for this September and were not asked. We received our table for 2 for the early dining, so we're good to go.
Just finished a Princess cruise, and this was how they operate as well. Your gratuity is automatically added to your stateroom charges, which was about $11 a day. We had some problems with our Maitre'D and dining, so only ate in the 2 Specialty restaurants and the Panorama buffet, which was a first for us. We had to see the purser 2-days prior to the last day to have the gratuity lifted, as we did not eat in the main dining room.
Rather than just remove the dining staff's gratuity, they "had to" remove the whole charge of $308, and then we individually passed out the gratuity to housekeeping, etc. My guess is, it may work like this.