可以使用 WooCommerce 提供的 WC_Shipping_Class 类来创建不同的运输类别。以下是一个简单的示例：

// 创建自定义运输类别
function add_shipping_classes() {
    $params = array(
        'id'          => 'small',
        'description' => '小型包裹',
    );
    $shipping_class = new WC_Shipping_Class( $params );
    $shipping_class->save();

    $params = array(
        'id'          => 'large',
        'description' => '大型包裹',
    );
    $shipping_class = new WC_Shipping_Class( $params );
    $shipping_class->save();
}
add_action( 'woocommerce_shipping_init', 'add_shipping_classes' );

// 在产品设置页面添加运输类别选项
function add_shipping_class_select_box() {
    global $product_object;
    
    if ( ! $product_object ) {
        $product_id = absint( $_REQUEST['post'] );
        $product_object = wc_get_product( $product_id );
    }

    $args = array(
        'taxonomy'     => 'product_shipping_class',
        'hide_empty'   => false,
        'show_option_none' => __( 'Select shipping class', 'woocommerce' ),
        'name'         => 'product_shipping_class[' . $product_object->get_id() . '][]',
        'id'           => 'product_shipping_class',
        'class'        => 'multiselect',
        'value_field'  => 'slug',
        'selected'     => $product_object->get_shipping_class(),
    );

    wc_dropdown_variation_attribute_options( $args );
}
add_action( 'woocommerce_product_options_shipping', 'add_shipping_class_select_box' );

// 在购物车页面或结账页面检查运输类别
function check_shipping_class( $package ) {
    $small_items = array();
    $large_items = array();
    
    foreach ( $package['contents'] as $item_id => $values ) {
        $product = $values['data'];

        if ( $product->get_shipping_class() == 'small' ) {
            $small_items[] = $item_id;
        } elseif ( $product->get_shipping_class() == 'large