I don't think you can update your application once submitted....however, if invited for an interview, I would definitely bring the records (i.e. logbook) to show what you have completed between the time your application was submitted and the interview.
Also, its POSSIBLE that you will get an interview sooner if you put HK as your first choice, but remember, if you do this you'll have to do ALL your interviews in HK and that might take a while. Also, if your choice is NOT Hong Kong and you make the later stages of the selection process, Cathay will pay for your flight and accommodation while in Hong Kong.