Hi,
you can only apply for an overseas ID if you are also applying for the Hong Kong SAR passport (and that you don't already have a HK ID).
1) To qualify for the passport (and the overseas ID)- you need to be a Chinese citizen.
2) About the overseas ID: as HKSAR passport holders MUST hold HKID by law, this means that those who wish to apply for the passport, but have not yet got the HKID, must also apply for HKID. For those who are applying overseas- they will be issued an overseas ID card- this card must be renewed within 30 days after the holder arrives in HK.
THUS- if all you want is the HKID card, applying for the overseas ID card would not be useful for you. (Criteria for applying HKID cards: pls see
www.immd.gov.hk)