Updating attributes via direct-SQL is unsupported, whether it is run through GEL or any* other SQL "tool".
If you want to update application data you should be using XOG, which can be called from GEL (or from any other technology that would support a SOAP call ; e.g. Excel VBA).
* technically, anything that can run SQL could update data, GEL is not anything special here apart from the fact we can run that via a Clarity process.