Caution - Do Not get renewed in HKG or overseas!
Others are correct that the US consulate in Hong Kong does a GREAT job getting a passport reissued in short order. The problem is that when you get you new passport, you are required to give the company 72 hours notice of a change in your passport number. Effectively you need to have 3 days off in HKG for this to be processed. If you have less than this time between reporting your new number, and returning to the USA as an operating crew member, you are not legal to operated a flight back home. The issue is not CX, but the TSA. The TSA requires 48 hours notice of a change in crew passport numbers, if your passport does not match the gen dec you will be denied entry and/or fined. CX uses 72 hours to ensure there is adequate overlap. The only way to return to the USA is on a paper ticket, hence PXing back home. Not good!
Spend the money and do it at home then you will avoid missing a flight and PXing home.