Hello Lloovurrad46
In terms of validity, the GA is the equivalent of the Swiss Travel Pass but for residents.
You can either choose GA or Half Fare Card as both grant you 50 % on upgrade tickets, so does the STP. Declaring the GA will simply reduce the available offers to class upgrade offers, this is why I recommended choosing the GA when holding the STP; it is a legal action.
Working as a ticket inspector myself, I would never recommend anything that would get you into troubles on board the public transport services.
Kind regards,
Roland