✔ 最佳答案
HKSAR passport holders can still hold HKSAR passport when they accquire other citizenships, unless they formally apply to change their nationality record with HK Immigration Dept.
It is illegal to use another passport to enter/leave US or AUS if you are citizen of the country. For example, if you are an Australian citizen and enter/leave AUS with a non-Australian passport, it is illegal under Australian law.
Australian government does not require dual nationals to renounce their non-Australian citizenships.