$WA_redirectURL = "https://www.cutestpetcontest.com/permThankYou.php?ProductID=1". (isset($_GET['EID'])?"&EID=".$_GET['EID']:"") ."";
<li><a href="https://www.cutestpetcontest.com/Products_Detail.php?ProductID=1<?php echo(isset($_GET['EID'])?"&EID=".$_GET['EID']:""); ?>">Cutest Pet Book</a></li>