that is just display and nothing in the mechanics, it can be done completely by default.
you just have to modify all tilesets with graphics of the new perspective and change the event sprites to fitting ones as well.
which is A LOT of work and requires a massive amount of graphics for the new tilesets, but nothing especially complex or problematic in general.
if you can get the new tilesets we can help you set them up, but I don't think anyone here has such tiles as the RMs usually use a different perspective than that one.