Allow a static page to show on a dynamic home blog page before the posts

You will need to edit your front-page template and before (or after) your loop, you need to make a call to get_post() so load your custom page. See the documentation for details.

You can then render your customisable page on the homepage.

For example, if your special page ID is 42:

<?php 
   $custom_page = get_post(42);
   echo apply_filters('the_content', $custom_page->post_content);
?>