How to change the headline title for an admin page in a plugin?

You shouldn’t need to hook anywhere in particular, simply output your heading at the start of your settings page callback and WP should position admin notices appropriately after your heading (there’s some logic written into the js/jquery).

For example i have lines like this at the start of various plugin settings pages.

<div class="wrap">      
    <h1><?php _e( 'My Plugin Name', 'my_text_domain' ); ?></h1>
    <?php settings_errors(); ?>

Some have additional or other markup, but the admin notices, whether they are Settings saved or error notices will render after the heading if it’s inside a wrap element, <div class="wrap"> in my above sample. You could move the <?php settings_errors(); ?> portion of my code above before the heading and WP would move the notice when it’s rendered.

I can’t recall off the top of my head where this is done in the core js, but i’ll have a dig and edit that info into this answer.

Later edit:

The WP admin javascript common.js sets up where notices are produced, here’s a link to the portion of code in core.