I doubt they would do that for you if you are simply transiting the airport for a short time. The airline might consider it if your DESTINATION was singapore by offering to change dates free... but otherwise flights are operating as normal.
Yes airlines operating as normal. Transit passengers who just will be in the air conditioned environment of the terminal are not going to be impacted by the haze. Maybe you will be if wanting to use one of the outdoor smoking areas, but tough. Those wanting to enjoy a holiday will be. Would definitely ruin it for anyone who had plans to sit by the pool at Marina Bay Sands.
Today it is has worsened again. Let's hope it will be clear by early July.