add_filter('angelleye_paypal_plus_shipping_line1', 'th_angelleye_paypal_plus_shipping_line1', 10, 2);

function th_angelleye_paypal_plus_shipping_line1($shipping_address_1, $order_id) {
    $house_no = get_post_meta($order_id, 'hausnummer', true);

    if (!empty($house_no)) {
        $shipping_address_1 = th_limit_length($shipping_address_1 . ' ' . $house_no, 100);
    }
    return $shipping_address_1;
}

function th_limit_length($string, $limit = 127) {
    if (strlen($string) > $limit) {
        $string = substr($string, 0, $limit - 3) . '...';
    }
    return $string;
}