Do something when admin posts a comment reply in WordPress.

snippet

/* Call the function when comment is posted */
add_action('comment_post', 'my_admin_reply');

function my_admin_reply($id) {

      /* Only do it when posting from admin */
      if (is_admin()) { 
      $mycomment = get_comment($id);
      $mycommentid =  $mycomment->comment_ID;
      $mycommentparent = $mycomment->comment_parent;
      $mycommentcontent = $mycomment->comment_content;
      
      /* Only do it when the comment has a parent */
      if (!empty($mycommentparent)) {
              /* Doing something with the comment contents */
      	      $mycommentarr = array();
	      $mycommentarr['comment_ID'] = $mycommentid;
	      $mycommentarr['comment_content'] = "Doing something!";
	      wp_update_comment($mycommentarr);
      }
    }
 }