whatever create model or update mode, you can set scenario like this, and use the scenario in validate

//create new
$user =  new User();
$user->setScenario('create');

//load exist
$user = $this->loadModel($id);
$user->setScenario('updatePass');


//load Model
/**
 * Returns the data model based on the primary key given in the GET variable.
 * If the data model is not found, an HTTP exception will be raised.
 * @param integer the ID of the model to be loaded
 */
public function loadModel($id)
{
	$model=User::model()->findByPk((int)$id);
	if($model===null)
		throw new CHttpException(404,'The requested page does not exist.');
	return $model;
}