<?php
$s = '<li id="item" class="list-item" href="#">Item</li><li id="item" class="list-item" href="#">Item</li>';
$find = "li";
$lenght = strlen($find);
$pos1 = strpos($s, $find);
$pos2 = strrpos($s, $find);
//Echo substr($s,0,$pos1) . "a" . Substr($s,$pos1+$lenght,$pos2-$lenght-1) . "a" . Substr($s,$pos2+$lenght);
Echo str_replace(array("<li ", "</li>"), array("<a ", "</a>"), $s);
preferences:
45.57 ms | 402 KiB | 5 Q