If what you mean is that, you open an account in sg and then trade sg stock in Malaysia, then Yes, for sure you can do that.

On an unrelated note, from a value perspective, I don't see much value popping out from Singapore. But, perhaps, traders have different thing that they look at and singapore, being more liquid may be a better market. But then, if liquidity is what some of you may be seeking, US perhaps is a better place?