The AM executives told me that I couldn't. It's a SET. So it's all or nothing. Which I find weird. Because the miles are charged based on the sectors. But then they said they don't offer mixed class upgrade. Yet they offered me to upgrade all or which sectors I prefered.

I called, I emailed Asia Miles and Cathay Pacific and their answers were all the same. Which I think it's ridiculous and there's nothing I could do about it.

So now there are seats available on 1 sector and I couldn't get it confirmed. And if 3 sectors cleared but one is not, they will also cancel the booking.