WordPress Filter for Mutating Title Tags

h2_to_h3.php

<?php

/**
 * This function mutates all H2s to become H3s. Add
 * this to your child theme's functions.php file.
 * 
 * Change or add to this as needed. I.e., change the
 * target tag and replacement tag to whatever you want.
 *
 * Add more lines to remove more title tags, if you want.
 *
 * Reference
 * - https://www.php.net/manual/en/function.preg-replace.php
 *
 * Examples
 *
 * Remove H2s Completely
 * - Change to preg_replace('/<h2>/', '', $theContent) and preg_replace('/<\/h2>/', '', $theContent);
 *
 * Make all H2s Become divs
 * - Change to preg_replace('/<h2>/', '<div>', $theContent) and preg_replace('/<\/h2>/', '</div>', $theContent);
 *
 * Change all heading tags to h3 while preserving any tag attributes.
 * - $theContent = preg_replace('/<h([1-6])(.*?)<\/h([1-6])>/si', '<h3 $2</h3>', $theContent);
 *
 * Don't forget to change the name of the function to keep 
 * it meaningful.
 */
function h2_to_h3 ($content) {
    $theContent = $content;
    $theContent = preg_replace('/<h2>/', '<h3>', $theContent);
    $theContent = preg_replace('/<\/h2>/', '</h3>', $theContent);
    return $theContent;
}
add_filter('the_content', 'h2_to_h3');