Is modding/modular files from users supported?

Title. Basically I want to make sure that, before spending many hours of my life in this engine, modular files from the community are possible to implement in the game that I create. IE: A rouge-like where there are set characters with their own stats/abilities. Is it possible for me to easily add support for the community to freely add their own files (like .json and .png) to a directory and have the game initialize and load them during the standard loading phase?

Engine is open. You can implement whatever system you like.
But it seems that you want the engine to do your work.

Yes, it is definitely possible to create your custom assets (with custom properties and compiler).

Could be useful if you’re making a very specific kind of game (i.e. a card game, you might want a “Card” asset with picture, stats, description, etc… so that game designer can iterate by themselves).