Change order item name of an existing order in WooCommerce
You need to use save() method as follow:
$order_id = 14851;$order = wc_get_order( $order_id );foreach ( $order->get_items() as $item ) { $item->set_name( $item->get_name() . ' Append This (S10)' ); $item->save();}$order->save();Woocommerce Documentation related methods: