Query on gst registration

QUERY ON GST REGISTRATION: - I have a query that whether it is possible for  a CA firm having different branches in the same state, can take separate registration under GST regime on a single PAN  for the convenience of Return filing? 

If it is possible, then what is the  procedure to take separate registration in case a firm already have taken  SINGLE REGISTRATION for all branches in the same state? 
Please reply!