在Auto Renewable Subscription中，修改订阅计划需要更新两个属性：新计划的productID和原计划的“cancellation_date”属性。如果没有更新“cancellation_date”属性，Auto Renewable Subscription会将计划续订日期视为取消日期。因此，更改计划后应更新该属性。

以下是使用Swift更新“cancellation_date”属性的示例代码：

func updateSubscriptionPlan(){
    let newProductId = "new_plan_product_id"
    let currentPlan = //获取当前的订阅Plan
    var originalTransaction: SKPaymentTransaction? = nil
    for transaction in currentPlan.transactions {
        if transaction.transactionState == .purchased {
            originalTransaction = transaction
            break
        }
    }
    
    if let originalTransaction = originalTransaction {
        let currentExpirationDate = originalTransaction.transactionReceipt?.expirationDate // 获取当前计划的到期日期
        let originalTransactionId = originalTransaction.transactionIdentifier // 获取原始交易ID
        
        let upgradeParams: [String: Any] = [
            "product_id": newProductId,
            "cancellation_date": "\(currentExpirationDate!.timeIntervalSince1970)" // 更新cancellation_date属性
        ]
        
        let appStoreReceipt = // 获取当前应用程序的Receipt
        
        let request = SKReceiptRefreshRequest(receiptProperties: appStoreReceipt)
        request.delegate = self
        request.start()
        
        let appleServer = InAppPurchaseHelper.sharedHelper().getAppleServer()
        appleServer.postUpgradeProductWithApple(originalTransactionId, upgradeParams: upgradeParams, withResponse: { (success, responseData) in
            if success {
                // 更新本地的订阅计划
            } else {
                // 计划更新失败，处理错误信息
            }
        })
    }
}