Set data to existing Shopping Cart Price Rule not working

I am using the following code to find an existing Shopping Cart Price Rule.

$pCoupon = Mage::getModel('salesrule/rule')->load($name, 'name');
$pRule = Mage::getModel('salesrule/rule')->load($pCoupon->getRuleId());

This works fine but when I try to modify its data there are no changes. The following code when used on a new price rule works fine.

if($pRule->getData())
        {

            $pRule->setDescription('MODIFIED');

        }

Is it even possible to modify existing price cart rules? My main objective is to modify conditions of that rule to support multilevel discount options. Any help would be much appreciated.