You can override the $page->create() method in a model, see this solution: Hook page.create:before, how to edit user input?
You can then set the changeSlug option to false in your blueprint to prevent editing of the slug.
You can override the $page->create() method in a model, see this solution: Hook page.create:before, how to edit user input?
You can then set the changeSlug option to false in your blueprint to prevent editing of the slug.