How can I add a new Magento store config data via template or block programmatically
You can use Magento core/config model to add new Magento store config.
$coreConfig = Mage::getModel('core/config');
$scope = "default";
$scopeId = 0;
$coreConfig->saveConfig('sectionName/groupName/fieldName', 'your value', $scope, $scopeId);