British Citizen changing visas in Hong Kong

I am a UK citizen (English if that makes a difference) and I'm planning on going to visit China on a L type. However while I'm there I will be waiting for a job offer for English teaching.

Is it possible to change L to Z in Hong Kong and/or Thailand or do I have to go to the UK and back to change? It's difficult to find a straight and relatively in- date answer on the Internet unfortunately.