Hi, Susan! Welcome to the Disney Parks Moms Panel!
As Timon and Pumba would say, “Hakuna Matata”! The
Disney Dining Plan is a fantastic way to prepay your meals and have no worries for the rest of your (Disney) days! The main reason that you are hearing conflicting information is that substitutions like this are based on the discretion of individual Quick Service locations, as well as the working Cast Member. For example, I was once able to substitute a dessert for an extra bottle of water (back when the Disney Dining Plan included dessert with each Quick Service meal), and later tried to do the same at a different location and was told that it was not possible. I believe that you would like to do the opposite, where you are trying to substitute the drink for a dessert, correct? As I mentioned, it is up to the discretion of the Cast Member and I have had friends be able to do so and heard of other Guests not being able to. If ever a substitution is not available, might I suggest selecting a bottled beverage to use at another time as they are quite portable and then use a Snack credit for your dessert? I always found that dessert with my Quick Service meal was too much for my family and ended up carrying our desserts out with us- but a bottle of juice, soda, or water is much easier to carry around a Disney Theme Park than a cupcake is! Spoiler alert: we ate many squished cupcakes- which were still delicious!
I hope this answers your question and that you have a wonderful vacation. Please come and visit us again real soon,
Jen