No, they don't have a policy where you can pay to refill a mug from a past trip. I think the reason is they want the profit from the mug. Soda cost then pennies to serve you, fountain drinks, tea, and coffee have a huge mark up rate. I know when I worked in the industry a glass of tea cost less that a penny, but they charge 2.50 a glass. Anyway, the mug probably cost disney about $1.00, and then they charge you 15 bucks. So they make 14 bucks. I highly doubt anyone drinks more that a dollars worth of soda while there, so they are making a huge profit. They want you to get the mug because the most expensive part of serving drinks is the cup it comes in. Disney wants people to buy mugs over and over agian, because they want the profit from the mug!!