What is the maximum allowed intensity for light beams pointing at the sky for non-aviation purposes?
Article 80(1) of the Air Navigation (Hong Kong) Order 1995 stipulates that 


  A person shall not exhibit in Hong Kong any light which — 
  
  (a) by reason of its glare is liable to endanger aircraft taking off from or landing at an aerodrome; or 
  
  (b) by reason of its liability to be mistaken for an aeronautical ground light is liable to endanger aircraft.
  
  Any such contravention is liable on summary conviction to a fine.


The full text of the regulation can be read here. 

Given this text, if your show is going to be anywhere near the approach or departure path to/from the airport (anywhere on Lantau Island, or east/west of the Gold Coast) you should probably refrain from using such lighting. I would strongly suggest you get approval from the authorities well before the event using an experienced local consultant, and prepare for that approval to be given or denied based on subjective analysis.