Originally Posted by
txflyer77
OP would still have access based on arriving in F, assuming that it's a same-day connection.
That's correct. Although it sounds like OP has booked an actual stopover, meaning the flight from HKG to BKK is not on the same day. If the aircraft is swapped for an aircraft without F, then I don't think you'll have much luck gaining access to Pier F, given that it's not a paid F ticket, etc.
But, who knows!
If visiting Pier F is REALLY that important to you, then I would switch the stopover to the inbound portion of your trip.