Can ‘edit_form_after_editor’ messages be varied for specific pages?

The edit_form_after_editor action delivers a (WP_Post) Post object as a parameter if you initiate the add_action the right way. After your function name you can set the priority and amount of accepted arguments (read more here).

function add_screen_message($post) {
    if($post->post_type=='page') {
        echo "<p class=\"edit-message\">Custom message here.</p>";
    }
}
add_action('edit_form_after_editor', 'add_screen_message', 10, 1);

The example above echoes your custom message below the edit form if the post that is edited is of the post type “page”.

I can recommend the site Hookr.io for great examples of how to use hooks and filters in WordPress. Hope it helps you moving on with your project.