How can I add custom code after html link

I am using WP All import for importing product to my wordpress site. I wrote this code

    $doc = new DOMDocument();
    @$doc->loadHTML( $html, LIBXML_HTML_NOIMPLIED | LIBXML_HTML_NODEFDTD );
    $imageTags = $doc->getElementsByTagName( 'a' );

    foreach( $imageTags as $tag ) {
        $tag->setAttribute( 'href', $tag->getAttribute( 'href' ) . '?xxxxxxxxxxx' );
    }

    return utf8_decode( $doc->saveHTML( $doc->documentElement ) );
}

but it does not works. Thanks for any hints