CX is quite good about it.... if you sort of plead 'guilty' and say that you're sorry but as CNY is coming up and your relatives in HKG are expecting lots of presents and you have to put them in another suitcase etc... CX , in my experience, will let you take on another piece if it isn't too big.

Worse comes to the worese, you might just have to pay for it. Just for the extra piece and it's not related to its weight. On transpacific flights, it's either $50 or $150.

But just try being 'nice' to the check-in agent first. It might work. Bring candy!