$order = Mage::getModel('sales/order')->load($orderId);
$shippingAddress = Mage::getModel('sales/order_address')->load($order->getShippingAddress()->getId());
$billingAddress = Mage::getModel('sales/order_address')->load($order->getBillingAddress()->getId());

$shippingAddress = Mage::getModel('sales/order_address')
->setFirstname("value")
->setLastname("value")
->setCompany("value")
->setStreet("value"))
->setCity("value")
->setRegion("value")
->setPostcode("value")
->setTelephone("value")->save();

$billingAddress = Mage::getModel('sales/order_address')
->setFirstname("value")
->setLastname("value")
->setCompany("value")
->setStreet("value"))
->setCity("value")
->setRegion("value")
->setPostcode("value")
->setTelephone("value")->save();