Some inclredibly helpful person here posted this answer -
If the Apply once and do not reapply option is selected, it changes this behavior, so the preference extension applies the results of the preference item to the user or computer only once.
however i must be too slow but i am not exactly sure what this ONLY ONCE mean :( Once ever? Or once per login session? Or once until something else happens?
REALLY appreciate clear explanation of this GPO setting