If HK immigration has ever seen that foreign passport before (perhaps when applying for HKID) then it will be linked anyway
I don't know whether their system would identify that you had an HKID if you got a new passport with the same personal details
If you want to enjoy subsidized public hospitals and work in HK, then I suggest you present your HKID when you become sick or at job interviews... if you lost or forgot it, then I suggest:
1) you go to HK Immigration and tell them what happened, so you can get a new HKID and prevent your passport getting flagged as overstaying
2) you leave HK within the period of entry granted as a visitor
Thanks for the prompt response. Reason why I asked is I am trying to determine whether it is possible for someone who holds a HKID as well as a foreign passport to enter HK using his/her foreign passport (assuming that it hasn't been linked to a HKID) to drive on the strength of his/her foreign driving license (regardless of whether he/she is in possession of a valid HK driving license).