Thanks for everyones input & insights.
As the original poster here’s my POV and the reason I asked: It’s a 17 day cruise, we have 14 speciality meals scheduled, we will have a butler & concierge. I wanted a way to ensure a set amount of $$ was for tipping for extra workers not included in the prepaid gratuities. My thoughts were to bring cash only for port shopping purchases.
Now that I know I can use refundable OBC for personalized tipping, I can go to guest services to apply and also also get a receipt. I plan to put the personalized tip receipt in small thank-you cards and hand deliver them to recipients.