Automatically add a character to field in edit post page

Here is one idea:

You could try to fire the change event of the #location-address (for example) input text field when the page has loaded:

function custom_jquery() {
    echo "<script>jQuery(document).ready(function(){

        jQuery('#location-address').on( 'change', function( event ) { 
            console.log('debug: on change fired!');
        });

        jQuery('#location-address').change();

    });</script>";
}
add_action( 'admin_head-post.php', 'custom_jquery' );

if your editing page is post.php.

You could also target another input field. To see the debug info, you need to have the console window open (in the browser).