This halves the shipping cost in the renewal order of the woocommerce subscription

gistfile1.txt

add_action( 'wcs_renewal_order_created', 'pi_modify_renewal_shipping', 10, 2 );

function pi_modify_renewal_shipping( $renewal_order, $subscription ) {

    foreach ( $renewal_order->get_items( 'shipping' ) as $item_id => $shipping_item ) {

        $total = (float) $shipping_item->get_total();

        $new_total = $total / 2;

        $shipping_item->set_total( $new_total );
        $shipping_item->save();
    }

    $renewal_order->calculate_totals( false );
    $renewal_order->save();
}