We have been 'upgraded' a few times, nothing of much value... but anyway
At HHI we were moved from a 1BR to a 2BR due to a litter box smell in our first room.
At BLT we were given one of the Lake View Grand Villas that had been a Theme Park View at one time. I can see how the view could be argued both ways - we could very easily see the fireworks from our windows and balconies - BUT it wasn't a straight on view.
At BWV we were upgraded from a garden view to a water view (I know those category names aren't right - I just can't remember the right names! HAHA)
We have been given Hospitality House rooms at OKW when we didn't reserve that category.
We never check in online, and we rarely if ever make view/room requests. It has worked out in our favor not to be too selective.
The only 'bad' room we have ever had was at AKV - Jambo - I felt like we were ACTUALLY walking to Africa each night. Our room was SO far from the lobby that I felt like there should have been a restroom and a snack cart, or at least a tram! We might as well have been at Kidani! HAHA
Anyway - it is possible, but there has to be a circumstance beyond their control before they will do it.
Rule of thumb, reserve the view you want, request something different at check-in, if it is available!