Is this possible?

Yes It is possible as when the asssessee applies the Dept will keep the same Number & add the services

Same number can be used for all services.

AS PER NEW SERVICE TAX NEGATIVE LIST REGIME IT WILL BE IMPOSSIBLE TO REGISTER OR ADD SERVICES IN YOUR SERVICE TAX REGISTRATION NUMBER. BECAUSE NOW THERE ARE UNLIMITED NUMBER SERVICES WHICH WILL BE TAXABLE SO THE CONCEPT FOR SPECIFC REGISTRATION WILL BE OUT  AND ONE REGISTRATION WILL WORK FOR EVERY KIND OF SERVICES

one registration is enough but he has to apply again to include for services.