the relevant part of the same is reproduced below:
Q7. I am an existing PAN-based Service Tax (ST), Central Excise (CE) and State VAT
assessee. I received the Provisional ID and password from the State VAT. While migrating
to GST through VAT on the GST Common Portal, I did not add my ST and CE details in the
Enrolment Application.
A: The facility to add existing registrations in the Enrolment Application is available on the GST Common
Portal. You can add the remaining registrations at the time of enrolment under GST. However, if you
have submitted the Enrolment Application with DSC or E-sign without adding the remaining
registrations, and have already received the Application Reference Number (ARN), you will not be able
to add the remaining registrations now. You will be able to add or remove the other registrations in the
Enrolment Application only after the appointed date (i.e., date of implementation of GST) through the
process of amendment (non-core).