如果在结账时选择了字段选项，如何加倍运费？

Question

I've found already many helpful code snippets for my WooCommerce 3 online shop.

Description/Example

If a customer buys 10 items and only 7 items are available he can choose (via a select field) to partially ship the order. If the option "Ja, teilliefern" is selected, the freight charges should be charged twice.

• At "regular shipping" 4,90 € -> 9,80 €
• At "free shipping" 0,00 € -> 4,90 €

Below is my current code:

add_filter( 'woocommerce_checkout_fields' , 'wp_bibel_de_add_checkout_fields' );

function wp_bibel_de_add_checkout_fields( $fields ) {
     $fields['billing']['billing_phone'] = array(
        'label' => 'Telefonnummer',
        'placeholder' => 'Telefonnr.',
        'required' => true,
        'class' => array('form-row-wide'),
        'clear' => true
    );


     $fields['billing']['billing_delivery'] = array(
        'type' => 'select',
        'label' => 'Wünschen Sie eine Teillieferung der verfügbaren Artikel?',
        'placeholder' => 'bitte auswählen...',
        'required' => false,
        'class' => array('form-row-wide'),
        'clear' => true,
        'options' => array(
            ' ' => ' ',
            'ja' => 'Ja, teilliefern',
            'nein' => 'Nein'
        )


    );

     return $fields;
}

add_action( 'woocommerce_admin_order_data_after_shipping_address', 'wp_bibel_de_add_custom_order_data', 10, 1 );

function wp_bibel_de_add_custom_order_data( $order ) {
    echo get_post_meta( $order->id, '_billing_delivery', true );
}