[HMBeaty]

Try this (tested and works on 4.1.8 Beta 1):

PHP Code:

if (in_array(STYLEID, array(1,3,8)))
{
    $link = array(
        'href="http://www.site1.com',
        'href="https://www.site1.com'
    );

    $word = array(
        'href="http://www.site2.com',
        'href="http://www.site2.com'
    );

    $this->post['message'] = str_ireplace($link, $word, $this->post['message']);
}