Adding markup to column text in “Edit Pages” admin page

I found that there is a filter, manage_posts_columns (and a related manage_pages_columns), that lets you modify the column headers on the “All Posts” admin screen. Using this filter is pretty simple, as the filtering function takes in an associative array with the short name of the column as a key and the heading as the value. You just need to return a modified version of the array, and you’re set:

function all_posts_modify_column($columns) {
    $columns['title'] = '<strong>Headline</strong>';
    return $columns;
}
add_filter('manage_posts_columns', 'all_posts_modify_column');