Actually, I don't think so. Our gratuities were pre-paid and we had them removed. They were not added to our account, it was actually the cruise line's policy (this was on Princess). Their only stipulation was, we had to settle this prior to the last full day on the ship. On =X=, we elected to have gratuities added to our account a few times, and other times we passed out envelopes with cash on the day prior to the final day.
Here is a picture of an inner office memo from a Carnival Accounting office, which was sent to me by a pax. You can see that certain guests requested to have the pre-paid gratuities lifted from their account (for whatever reason) and were accommodated.
I just checke the =X= website, and at this time they state gratuities are added on a daily basis and can be modified if the pax chooses.
I guess it's all moot at this point, since they removed the new dining option...