Success!
On a recent trip I had a one-way ticket IST-TLV booked in economy (Q). I was arriving to IST on a separate ticket so left a wide margin between the two flights. As I arrived in IST I realized I had some 3.5 hours for my TLV flight, but there was an earlier flight in 2 hours. I asked the lounge agent whether it would be possible to move to the earlier flight, and within 2 minutes I had a new boarding pass. Very happily surprised! (I'm Elite, not sure if it mattered.)
Shuly