$re = '/(.*?)PLC\.com(?:\/\ben\b)?(.*)/m';
$str = 'https://www.mycompanyPLC.com/en/lorem/ipsum/whatever
https://www.mycompanyPLC.com/lorem/ipsum/whatever
http://www.mycompanyPLC.com/random/query/url
http://www.mycompanyPLC.com/en/random/query/url
ftp://www.mycompanyPLC.com/en/random/query/url
';
$subst = "$1LTD.com$2";
$result = preg_replace($re, $subst, $str);
echo "The result of the substitution is ".$result;
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php