You can't have more than one certificate of authenticity template per account: your account has a single set of brand details — artist name, shop name and logo — which apply across all your work, so you can't set up multiple templates each with its own artist name and logo.
What you can vary per drop
You can vary the signature per drop. Keep a Signature Library in your Media Library with multiple signatures, then select the right one for each drop. This lets different artists' work ship with their own signatures on the certificate.
If you need more than one certificate of authenticity design
If you need different artist names and logos on certificates, the only solution is to run separate accounts for each artist.
For details on setting up signatures, see the Signature Library feature in your Media Library (left sidebar).