I believe the bread can no longer be edible. Otherwise, it works backwards & is bad for parnasah. And there is also something in kabbalah about never throwing ANYTHING out that is still useable/edible. It’s very bad & we’ll leave it at that.
Either way, I’ve seen people hear this segula on Shabbos & they get so excited that they throw the crumbs out to the birds. I’m pretty sure it says in the Shulchan Aruch that you can’t feed birds that you don’t own on Shabbos. But I would ask a rabbi to make sure.
Either way, I prefer to feed fish.