I have four flights booked (2x BKK-SYD-BKK)
Two were booked on TG475 & TG476, so no changes to those.

The other two were booked on TG471 & TG472.
The UA website showed F class award seat available on TG476 on the same day as my TG472 flight, so I was able to get switched over to that flight.
On the day of my TG471 flight, there's no award availability showing in any class on TG475. No F class award seats on TG475 the day before or after, nor are there any F class seats open the day before or after for my FRA-BKK flight connecting to BKK-SYD, so it looks like I'll have live with the 773 on BKK-SYD for that itinerary (at least I have F class on the A380 from FRA).