xdan0920
Think for yourselfer
I'm not sure I follow... the Haunted Mansion overlay is a complete overlay of queue, ride and script in it's entirety and it certainly is impactful. It becomes a different attraction. Because the script is changing I assume there could be a way to build the script around decore along the route if they so chose. Doesn't sound like it but it'd be fun if done right.
Like @NowInc said, it wouldn't make sense for the natural environment to be decorated.
If you are thinking a complete makeover, that's another story. You want to make a Christmas Cruise and overlay everything, that can be done, but it's a HUGE investment. The Temple becomes the NorthPole, there is snow on the ground, Polar Bears instead of Hippos, ect...