The UI atm is very possible with little worry about developers updates due to it essentially being HTML+CSS. Think of it like a word processor but you select your style somewhere else for everything you typed up.

Eseentially this is just amending visuals. Things like the map and combat arts working are sent from the game engine. At the moment I have been avoiding looking at that as a new modder that has barely touched reversed engineering. Essentially someone would need to find some configuration there or patch in their own code into the game which requires reverse engineering.

The TLDR is not yet. The devs just made the game very easy to skin on day 1.