Provide a better way to update FTB modpacks

Would it be remotely possible to have a cleaner way of updating my curseforge modpacks? Maybe have an environment variable to called `update-pack` or something that would remove the mods and configs folder and then re-download them from the file specified by `CF_SERVER_MOD`? Currently, I just remove the `FeedTheBeast` folder which also resets all character levels, which is pretty annoying. I understand that many packs do things differently but maybe it would be possible to just download/copy over the updated mods and configs and delete everything else?

Start by locating the startup logic that handles CF_SERVER_MOD and the FeedTheBeast directory. Determine how an update-only operation should preserve character data while refreshing mods and configs, then verify that the existing modpack installation behavior remains unchanged for other packs.

Written by the indexing model from the issue text.