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>>>>I would unscrew the knob and take the valve apart carefully, stopping as soon as I hear some air coming out waiting as long as needed until the pressure comes down to 14 PSI.
Yes, exactly like this.
It does not matter what the valve looks like.
It has a knob and a way to reach inside it.
Once the tank is empty you can remove the regulator and nothing is damaged.
BTW I'm in Brussels now on a business trip.
Very nice city with very friendly people.