Can this mod be used in an existing save or does it require a new map generation?

To be honest, I'm not sure, I'd assume newly generated chunks would utilize the new ore patches. But unless you also include More Galore it won't actually add any uses for the new ores even if they do spawn. This mod ONLY adds the ore, if you want the ores to be usable you'll need More Galore. And as More Galore changes almost every recipe, it'd almost certainly break an existing factory save. Highly recommend a fresh start.

Thanks. Sounds fun to start a fresh game also with foodtorio. Recovering from Py and this could scratch the itch