Hi mwong9413, I'd like to answer your question rather than nose as to why you want to do it or annoyingly give my opinion on whether I think its a good idea or not!
a.) China require you to give up your British Citizenship, fill in the forms, go through the motions, get your HKSAR passport.
b.) Britain does not recognise renunciation of citizenship in this situation - you don't have to reapply for British citizenship, you never lost it!
c.) I know this because I am taking my sons through this process currently.
I also know people with HK passports and o/seas passports. Not 'guess', not 'think', know! Thanks!