as i understand it (someone correct me if i am wrong)... 
if your ethnicity is Chinese and you were born in HK, then you are a HK Permanent Resident with ROA and entitled to a HKPIC.
and you will never lose that status regardless of how long you are absent from HK (unlike overseas-born Permanent Residents who lose ROA if they are absent for >36 months.
in fact, you will be regarded as a Chinese citizen and your foreign passport will be regarded only as a travel document within Chinese territory, ie. you will not be entitled to foreign consular protection due to your foreign passport.
the only way you will lose HK Permanent Resident/ROA status is if you formally renounce your Chinese nationality, in which case you will be downgraded to RTL.
it's best to return to HK to do it (go to Wanchai Immigration Tower). i think you just need your HK birth certificate (although it will be wise to bring everything else - old passports, parents' documents, just in case you are asked for them).