So far as I can tell this still requires an pass/wallet signing certificate from the apple developer program to use, so you can't use it to create ad hoc passes, unless you already have a $100 developer subscription.
But if a company already has their own custom app for their bonus card, that means they already have the developer subscription
If you’re on ios27, you can create ad-hoc passes on the phone from the Wallet app and customize it as needed.