Technically they don't,but if you ask nicely and they have some spares (which they normally do) they would not refuse you.

Is it worth it? BKK-HKG is a full hot lunch service,HKG-BKK is a late night cold snacks service. In Y it's a cold snack service both ways. It's a flat bed in J in any case (A332 or B787),but Y on 787 is still super comfortable,unlike 332.

The fare diffirence is what? 5000THB/140USD? It's probably worth it,but I personally stick to Y on this route...but then again I am Emerald with RJ and get access to the CX lounges both ways (I would happily pay 100USD just to to go to The Pier F) and I get Premium Lane (BKK) and priority check in/boarding anyways which is vital in airports like BKK. They also block the adjacent seat(s) for OWE and I know all the crew operating the BKK flight,so I don't really need more comfort/attention/food&drink. I also don't need extra miles/tier points/credits or whatever,but this maybe an important factor for some on this board.

Regards
Rami