Custom tag page hook

/* Replace template with newsletter template if tagged with "road runner" */
if ( ! function_exists( 'newsletter_template' ) ) :
function newsletter_template( $template )
{
    if( preg_match("/.*road.*runner.*/i", get_query_var('tag')) )
    {
        $new_template = locate_template( array( 'newsletter.php' ) );
        if ( '' != $new_template ) {
            return $new_template ;
        }
    }

    return $template;
}
endif;
add_filter( 'template_include', 'newsletter_template', 99);