I did this and it worked well.
I had read all the warnings on here prior to my Feb 2024 cruise about registering a debit card as your onboard payment card, because the holds could be in place for a month, thus preventing me from using my own money. I have a regular Mastercard account which I don’t use much and it incurs regular international conversion fees. I also have a debit Visa card that has no international conversion fees. I decided to register the Mastercard on my onboard account, so any holds would be put against that card.
The evening of the last full day onboard I visited guest services and asked to pay the outstanding balance down to zero using the Visa card. They had to register the Visa so they could take the payment from it. They completed the transaction bringing my onboard account back to zero. Then they removed the Visa card from the system. They still had the Mastercard registered to cover charges in the last 12 hours, although I was pretty confident there wouldn’t be any extra charges at that point.
It took about 15 minutes to get it sorted.