<?php

$pattern = 'qw_er00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000 ';
$replacement = 'id_alien';
echo substr_replace($pattern, $replacement, 0, strlen($replacement));