I declare that, as an employee of the Government of the Hong Kong Special Administrative Region of the People’s Republic of China appointed on non-civil service terms, I will uphold the Basic Law of the Hong Kong Special Administrative Region of the People’s Republic of China, bear allegiance to the Hong Kong Special Administrative Region of the People’s Republic of China, be dedicated to my duties and be responsible to the Government of the Hong Kong Special Administrative Region.
Yes it is impossible to emigrate to China. China does not grant citizenship to foreigners.
If you want to work there, sure. You can, though it's a pain in the ass. But you'll be an expatriate, not an immigrant. Important difference.