No. They won't need to apply for fresh GST registration. The GSTN would migrate to all assessees or dealers to the GSTN network and would issue a provisional GSTN certificate with the GSTIN number on the appointed day, which after due verification by departmental officers in 6 months would get converted to the final registration certificate. The registrants would be required to submit the required documents for the purpose of converting a provisional certificate to a final certificate within the given timeframe
Service tax assesses who have centralised registration would need to apply afresh though in those states where they operate their business.