Let's say I want to do R -> U for something like ORD-HKG-(stopover)-HND. ORD-HKG-HND and ORD-HKG is the same mileage band so ideally I want to upgrade both sectors. It's in the same ticket, ex-HND.

Suppose ORD-HKG clears, I get charged 27.5k AM but HKG-HND (on some future desired date of mine) is waitlisted. When HKG-HND eventually clears a long time later, do I get it for free or will I be charged the R->U mileage for HKG-HND again separately?

If that happens, to avoid that, should I change the underlying R booking of HKG-HND to some date where it also has U availability so both segments will clear at the same time once ORD-HKG clears. But then once that happens am I locked in for the date to travel HKG-HND? Can you change an R->U sector date once it's cleared?