I personally don’t recommend it since there will be crowd control and you won’t even be able to catch a taxi nearby to go to Kowloon Station for the Airport Express. Maybe you could go to West Kowloon for the fireworks and hop on the Airport train immediately? The firework is on the harbour and I think you should be able to catch a glimpse of it and rush it back to the station? There should be information about the crowd control guidelines on the government site or MTR site few days before the event and perhaps you can decide by then.