The tech doesn’t work this way. And what you’re trying to do doesn’t make sense to me.
You can create a catch-all address and have an autoreply with a polite massage.
But a bounce happen when there’s no way of successful delivery. Delivering to a catch-all address is a successful delivery. You can’t have a mail delivered to an address and have it bounce back at the same time (Electronic or Postal).
If someone accepted your mail, that’s a delivery. And a delivery is a delivery.
I have concluded that the blunt bounce message is provided by the client email program - after all if the sent email cannot reach a destination then how could it be generated there? So the bounce message is not editable? I had thought that “domain only” (@domain.com) messages were handled by some default alias (eg firstname.lastname@example.org) as they must reach the server - otherwise the catch-all would not work. This must be the correct conclusion or there must be a default bounce message on the server!
You’re so confused. And clearly you don’t understand how this works. If I were you, I would stop trying to come up with theories. And try to learn things as is. I thought about skipping this topic because it doesn’t make any sense. Rather stupid if you ask me. But this is going to live on internet as long as this forum is alive.
When you’re sending an email, the destination is the recipient’s mailbox. You assume it’s the client mail sever. But it’s not. Client mailserver tries to deliver it to the recipient, and when it can’t the email bounces.
The keyword here is “deliver”, this doesn’t mean that the recipient mailbox doesn’t exist. Recipient mailbox could exist and email could still bounce. Because the mail can’t be delivered for some other reason.
I’m not saying you can’t edit a bounce message, you could if you have correct programming skills. But bounces have more important use-case in sender reputation. So it’s better to leave it alone.