When can I switch my US First reward to fly Etihad?
 

Does anyone know?

I am flying First Class

LAX -> SFO -> Haneda
NRT -> CGK
CGK -> HKG -> LAX

But on the last leg, I need to add a day. Cathay doesnt have any availability right now ( Summer travel), so I was curious..when can I change the award (with fee) to fly Emirates?

Emirates is neither a partner of AA nor of US , so why would you think you could change to it?

I haz feeling OP was referring to Etihad...

If it relates to changing to EY, I would expect that once the US scheme ends, then the existing award will need to be cancelled and recredited to AA and then a new award can be booked in accordance with AA rules and costs

When you say change to Etihad, you mean just one segment? The answer to that has to be no.
Even if they were together I feel AA books Etihad tickets different, because I had a flight from AUH to SYD, and wanted to add on a segment inside Australia and they said it was additional miles. So not the same as their normal ticket.

That would likely be that EY did not offer fares to that domestic location which allowed travel on an airline that is a partner of AA

Not only does it have to be a valid airline for awards, but the governing carrier has to have a fare that is valid for the itinerary

Taking LHR-ADL as an example, EYs fares require that the domestic sector be on EY ( codeshare ) or on VA . Since VA is not a partner of AAdvantage that will stymie booking the domestic leg

So what is the best way to determine if AA miles can be used to book a specific EY itinerary? Try to book it on EY ticket stock (via any OTA) and manually confirm all non EY segments are AA partners?

Expert Flyer is pretty good at listing valid routings

e.g. for AUH-ADL here is an extract of the valid routings list

Looking at this EY fare from Abu Dhabi to Adelaide, can see that the domestic sector has to be on EY,NZ or VA. Within Australia EY has no flights of its own , only codeshares on VA. To use a through award, the domestic flight to Adelaide would need to allow travel on Qantas

Not quite so easy is perhaps to price up on ITA a desired routing and see if it comes up as a single fare componant or if there is a break in the fare

Is there a situation in which it is possible to book using AA miles on EY and have a connection on another carrier? Like, Europe or Africa or Asia? I guess Dave showed us it is impossible for Australia

The rules change for awards made using non-oneworld partners, so this might invoke redeposit, fees and a new award in AA policy. It may differ from USDM, but the substitution of a non-oneworld segment may create some problems under oneworld award policies (which normally do allow change of oneworld carrier) iirc.

Dave Noble knows this stuff better than I, so it's good he's reading this thread and can correct me.