I do have checked baggage from my inbound flight into Bangkok, so I have to go Land side anyway.
I have no problem in paying a small fee for the change, the main problem I assume is, that I’m booked on a Etihad Award ticket. BKK-USM in C, though this is the only flight segment on the ticket.
I wouldn’t have any problem taking a Y seat as well,

im just not sure who’s in charge here of actually deciding whether it’s allowed to waitlist me. Etihad or Bangkok airways.