Well PKHeX won’t support saves from hackroms, cause the data can be radically different. Also, just a personal guess unrelated to the devs, if you allow one hackrom, it’ll open the floodgates and everyone will want their hackroms/favourite hackroms supported. It’s just cleaner to stick to official games.
thanks for the link, I’ll check it out later.
also, you mentioned something about types? Types aren’t in the Pokémon data outside of Gen 1/2, so you can’t edit that via save editing.