如果唔係過多排要整working visa都唔會的起心肝續 - As a BN(O) passport holder, you can register to vote in all UK elections if you have an UK visa which allows you to stay in the UK for more than 6 months.
應該點都一出世就有香港居留權掛 - having 香港居留權 alone does not mean that you have BN(O) status.
Anyone born in Hong Kong before 1983 would automatically become a CUKC under the British Nationality Act 1948. CUKC became British Dependent Territories Citizens for most Hong Kong people in 1983.
For those who were born in Hong Kong on or after 1983 - if at the time of your birth, one of your parent (either father or mother) was a Hong Kong permanent resident or a British Dependent Territories Citizen , then you would receive British Dependent Territories Citizenship at birth.
A British Dependent Territories Citizen will need to apply for a British National (Overseas) passport before September 1997 in order to have the right to use a British passport after the handover.