I find it's very easy in Shanghai (where I always use AM tickets), they proactively asked last weekend if I wanted to get on the earlier flight (good, because it was the new KA interior with the full AVOD) and nodody has ever mentioned a change fee. In TPE I usually do turnarounds there and I find that when I arrive if I go to the gate of the next departing flight (because changing planes at TPE is so quick) and ask, the answer is often 'we did check and your ticket doesn't allow a change", which is fine, I have to sit in TPE or in HKG before my JFK flight anyway - again it's always an AM ticket to TPE and an I class out of TPE (the one I'm asking if I can change). But if I walk to the lounge and ask there, the answer is always yes (assuming there's space or likely to be space) and they just change my I class ticket so I guess it does depend on who you ask :-) But generally, very helpful.