[php]
/* Change COD default order status to "On Hold" instead of "Processing" in Woocommerce BEGIN */
add_filter( 'woocommerce_cod_process_payment_order_status', 'change_cod_payment_order_status', 10, 2 );
function change_cod_payment_order_status( $order_status, $order ) {
    return 'on-hold';
}
/* Change COD default order status to "On Hold" instead of "Processing" in Woocommerce END */
[/php]