You don't need permits to ship diffusa/bridgesii across state lines, at least not anymore. So ship with confidence! The itty bittys could be left behind and they'll live through the plague, nuclear war, whatever.
They are probably common "pest" snails, and while they do help keep a tank clean, they can mulitply faster than rabbits. If you really want to, you can ship them too because they aren't one of the prohibited species. HTH