Magento隐藏运输方法或通过观察者更改其价格

Question

I have created a Magento module with an Observer that should hide a certain shipping method, but I can't get it to work.

class Company_Modulename_Model_Observer
{
    public function hideShippingMethods(Varien_Event_Observer $observer)
    {
        if (Mage::getDesign()->getArea() === Mage_Core_Model_App_Area::AREA_FRONTEND) {
            $quote = $observer->getEvent()->getQuote();
            $store = Mage::app()->getStore($quote->getStoreId());
            $carriers = Mage::getStoreConfig('carriers', $store);
            $newPrice = 10;

            foreach ($carriers as $carrierCode => $carrierConfig) {
                if ($carrierCode == 'flatrate') {
                    $store->setConfig('carriers/flatrate/price', $newPrice);
                    $store->setConfig('carriers/flatrate/showmethod', '0');
                    $store->setConfig('carriers/flatrate/active', '0');
                    $store->setConfig('carriers/flatrate/title', 'Test title');
                }
            }
        }
    }
}

Of all the setConfig settings only the $store->setConfig('carriers/flatrate/title', 'Test title'); works.

So the title of the delivery method gets changed in the checkout, but the price doesn't change and it is still shown.

How can I hide or change the price of a certain shippig method?