Feature request for an option to copy custom advancement jsons from somewhere in the config folder to every new world created. This may be outside the project's scope. Would help modpack makers and players who want custom advancements for every new world.

onWorldCreate(worldfolder)
{
  if(config.copyadvancements)
    copyFolder(config.advancementpath, worldfolder+"datapacks");
}

Although I only tagged this like 2 days ago as a feature I have been thinking and this is indeed out of scope. I think I will stick to cosmetics and QoL changes. Modpack makers might be better of using something along the lines of Triumph.