First off I think you've done a really good job here! This system module is by far the nicest Fate module I've found. The official one is all over the place in terms of readability not to mention bugginess while yours is clean and really easy to follow, well formatted.

However, I would like to do extensions to run FateX as base for the custom Fate my RPG group runs. I've experimented a little with editing FateX directly instead of just building a Module to override parts of it but since FateX uses the older scripts method of loading things into FVTT it's difficult to hook into things like DataManager.getAvailableSystems. Either that or I am not seeing where I should hook into things.

Is it me that is doing something wrong, or is it possible for you to export things from FateX in a future release so that we can override parts or all of it with modules? I'm not new to JS/TS but I'm somewhat new to extending FVTT so it might just be me looking in the wrong place.

Really what I would prefer to add is a separate Stunts track for spells and a few other settings and resources that our group uses. I started modifying the official Fate system for this but it's so clunky xP. I also dropped a new json file under /systems and added it to systems.json but FateX throws errors since it doesn't recognize the new fields (not surprisingly!).