To the OP, did you read the fare rules upon booking?

Im not sure you're correct in your assumptions. Some I fares from Japan are extremely restrictive when I was looking - I absolutely have seen no changes allowed, or extremely high penalties like the guy above mentioned. They are some of the most onerous in all Asia for CX, IME.

You can't just pull random change fees down from the internet and say they're applicable to your ticket...you need to read your fare rules as written that came with the ticket! It's true CX had those crappy "business save, business flex, etc" terms but I don't know if that refers to I fare, D fare or C fare. It's possible your ticket isn't included in those terms you found on the internet, especially if you bought during one of those ex-Japan super cheap I fare specials. In those cases I have seen fares that don't allow changes.

I know this doesn't help you now but you gotta read them before you book! You can't just find a good fare, buy it and cross your fingers you can change it, add stopovers, etc. Sometimes it can be hard to reach CX....although it's kinda inexcusable you didn't email them, because both Japan and Taipei reservations are excellent in response, IME (!! This isn't the US!)...but you really should know the terms of the ticket if you're buying cheapo tix. I guess it's good to know.

My gut says the title of this thread is going to prove incorrect, unfortunately. Hopefully not but....I could see it possible this ticket is highly restricted.