Of course Ho Sau Nan. You say you are living in Wong Tai Sin. So you can choose either Wong Tai Sin Net or Kowloon City Net in the future S1 application.
If you now choose Grandmont, only Wong Tai Sin Net will be available for you in the S1 application unless you move home.
If you study at Ho Sau Nan in the Kowloon City Net, but eventually choose the Wong Tai Sin Net in the future S1 application,I believe the chance of being downgraded in the banding may not be so high.