No, that's all wrong, Bruce.
It's actually possible to disable the green messages with a registered version of FSUIPC. But obviously, it's not possible to choose all the individual messages which can appear from, but it's set up as a general green bar message disabling function. Therefore, you can't just deactivate GSX messages only, either everything or nothing.
I have the registered version of FSUIPC, but if I recall correctly the disabling of these messages is no longer possible in FSX through FSUIPC, it only worked in FS2004.