<?php
//Store your html into $html variable.
$html="
<html>
<head>
<title>Untitled Document</title>
</head>
<body>
<a href='http://example.com'>Example</a><br>
<a href='http://google.com'>Google</a><br>
<a href='http://www.yahoo.com'>Yahoo</a><br>
</body>
</html>";
$dom = new DOMDocument();
$dom->loadHTML($html);
//Evaluate Anchor tag in HTML
$xpath = new DOMXPath($dom);
$hrefs = $xpath->evaluate("/html/body//a");
for ($i = 0; $i < $hrefs->length; $i++) {
$href = $hrefs->item($i);
$url = $href->getAttribute('href');
//remove and set target attribute
$href->removeAttribute('target');
$href->setAttribute("target", "_blank");
$newURL=$url."/newurl";
//remove and set href attribute
$href->removeAttribute('href');
$href->setAttribute("href", $newURL);
}
// save html
$html=$dom->saveHTML();
echo $html;
?>