Originally Posted by
number_6
The fare difference will most likely be between USD 1000 and 2000 if it can be calculated at all (depends on your fare basis). Having flown F HKG-TPE dozens of times, it really isn't worth it esp. as the meal service has been downgraded to be similar to J. Also some chance of EQP so that no F operates on your flight. Good luck, if you are determined to do this then you will either have to go landside to the service desk or sometimes the F lounge manager will do this for you (but if you are only QFF gold than no F lounge access).
Can't be.
I can't imagine upgrading HKG-TPE from J to F can be US 1000 to US 2000 one way. This will be more expensive than the one-way F itself (which is about US 950 whereas Business class is about US 800.
Irrespective of status, don't J passengers have access to J lounge at CX? I am sure they do. You can surely ask the J lounge about upgrading to F. No reason why only the F lounge can deal with upgrading to F.