Hi Sylvain,
with the introduction of the EyeX SDK we also saw the need to clarify the role of the Gaze SDK, because we cannot have two SDK offerings that overlap too much. To cut a long story short: we decided to deprecate and remove all configuration management from the Gaze SDK, that is, the entire EyeTrackerConfig subsystem.
So, at this point, you have two choices: either migrate to the EyeX SDK, where all configuration matters are taken care of by the EyeX Engine (as a an EyeX client application you basically assume that the eye tracking just works). Or stick with the Gaze SDK and take care of the entire configuration matter yourself in your application.
I cannot recommend one or the other without knowing more about your particular application, but you are of course welcome to continue the discussion here on the forum.