No, we don't allow changing of gain or offset through SGP other than the ASCOM properties dialog (which we have no actual control over other than to show it). For ASCOM devices SGP should be pretty "dumb" as far as the inner workings of the camera are concerned (kind of the point of ASCOM actually). SGP requests an image for X amount of seconds and after that time the camera delivers it. We can set somethings like the binning, subframe and such but for the most part the inner workings are not exposed to us.
Thanks,
Jared