This actually applies in America and Europe, also. It's literally illegal to fit HID in a Halogen reflector. Headlights are made to very specific standards and they have to have a DOT or E-code approval stamped on the glass to be legal. Cars or motorcycles, the same is true.
The same applies for LED "bulbs" in the stock reflector, also illegal everywhere.
You are probably allowed to replace your headlights with approved LED reflectors (reflector with built in LED, made in a factory, and DOT and E tested) - JW Speaker, Vision X etc. Not sure if that's true in Singapore, but it is in Europe and the USA.
Headlights need to work properly or they'll blind motorists and cause accidents, so they're heavily regulated.
@mousseman - if you do LED right per the above (for example JW Speaker 8700 or 8790 if you have the cash) it will absolutely pass. They're E code tested and approved.