Programmatically change Magento’s core config data

$configValue = Mage::getStoreConfig('sectionName/groupName/fieldName');

sectionName, groupName and fieldName are present in etc/system.xml file of your module.



$testSwitch = new Mage_Core_Model_Config();
/*
*turns notice on
*/
$testSwitch ->saveConfig('design/head/demonotice', "1", 'default', 0);
/*
*turns notice off
*/
$testSwitch ->saveConfig('design/head/demonotice', "0", 'default', 0);

Well explained at http://inchoo.net/ecommerce/magento/how-to-programmatically-change-magentos-core-config-data/


Get the core config data collection that match the path and update new path:

try {
        $path = 'old';
        $collection = Mage::getModel('core/config_data')->getCollection()
                        ->addFieldToFilter('path', array('like' => $path . '/%'));
        if ($collection->count() > 0) {
            foreach ($collection as $coreConfig) {
                $oldPath = $coreConfig->getPath();
                $newPath = str_replace("old", "new", $oldPath);
                $coreConfig->setPath($newPath)->save();
            }       
        }
    } catch (Exception $e) {
        Mage::log($e->getMessage(), Zend_Log::ERR);
    }
Read more about Core Config data at http://alanstorm.com/magento_loading_config_variables