Nope, sorry. Apps are usually much more expensive than the dessert options so swapping them is not possible.
True that it's not allowed. But not really so much more expensive. At the very least, soups and salads are about the same prices as desserts.
Primetime Cafe -- Iceberg wedge, $5.49. Chicken noodle soup, $6.49
Desserts -- $5-7.49
Tony's Town Square: Mixed Greens, 5.49. Caesar -- 5.99 Soup -- 5.49
Desserts: $4.99-6.49
One theory is that they want to turn over the tables more quickly, so they don't want to encourage 3-course meals fully covered by the plan.
Another theory is that desserts are much higher mark-up then soups and salads. So Disney's price might be $1 for the dessert.. but $3 for the appetizer... so it makes more sense for them to give away the dessert.
Another theory is that it would simply be too confusing to allow swapping.
Another theory is simply, they are being cheap. They saw a chance to cut out an allotment, so they took it. Just like they cut snacks down to single-serve items, even where the multi-serving was under $4. Just another chance for them to slim down the
DDP.
Or some combination of all these theories.