If you don’t load your legacy when the mod is installed that save should be fine. If you want to go back to it later, just move the mods folder to your desktop and clear caches before loading up the game. As far as questions go, I’d ask the modder directly on his discord, or if you use Twitter there are some helpful folks there as well (let me know if you’d like those links). :)
Edit: you can also make a copy of your save and put it somewhere safe just in case.