WordPress - Disable saving in the customizer

functions.php

<?php

/** Add this to the bottom of your functions.php file in your theme **/

require_once ABSPATH . WPINC . '/class-wp-customize-manager.php';
remove_action('wp_ajax_customize_save', array($GLOBALS['wp_customize'], 'save'));
add_action('wp_ajax_customize_save', 'return_403_on_customizer_save');
function return_403_on_customizer_save() {
        wp_send_json(array('message' => 'Theme Editor in Read Only Mode'), 403);
}