Actually they could use the same system than 2013 and newer Nissan Leafs use, although on a larger scale of course (although probably not too much larger, depending on the size of the cabins), which is basically a heat pump:
https://www.nissan-global.com/EN/TECHNOLOGY/OVERVIEW/heat_pump_cabin_heater.html
Overall this would need minimal amounts of electricity compared to a traditional AC system and it would be relatively lightweight, plus it could provide heat during the colder periods all from the same unit.
So in other words, it could be done with a little bit of engineering, which Disney is quite capable of doing. Given the size and the fact that I would assume that there are already going to be heaters for the colder periods, I would think that Disney could even add these in after the fact if necessary, but I would think they would want to get it right from the start.