You have to give in writing to the jurisdictional assisstant commissioner or deputy commissioner of central excise.
W.e.f 1.3.2007 the superintendent of central excise has to issue a fresh certificate in Form ST-2 with in 7 days of the intimation of addition of new services
If the service provider who is already having registration for S.T. n starts providing new service he should inform the Supritendent and get the Regtn Certificate endorsed suitably.
So Supritendent of Central Excise sahll issue Regtn Certificate within 7 days from Date of Receipt of appln.... in Form ST-2 and if not given within 7 days then it shall be deemed that regtn is granted .