Hi James!
Thanks for reaching out!
There is no built-in functionality to achieve that, but it is possible to get that kind of functionality with some custom coding.
I’d recommend you take a look at the tickets.php template file located at wp-content/plugins/event-tickets-plus/src/views/wootickets. You could make a template override of it and add a message line 150 where the Out of Stock! message is rendered.
Additionally, you might want to check the WooCommerce backorders functionality > https://docs.woocommerce.com/document/managing-products/
I hope that helps. Let me know if any follow up questions.
Best,
Victor