Hi @rtu
Thanks for reaching out to us and welcome to the Zoom Developer forum, I am happy you are here!
This is an interesting use case.
I would think that if they have a Zoom account already, the networking profile in the lobby will be the one they have set up in their own account.
I do not think that if they use the email that they have connected to their Zoom account, it will rename them if you are appending the @johny19 in your registration form (at least this won’t change on your end if that makes sense, it won’t change in your reports lets say)
I think that a good way to track participants is by leveraging the registrant_id but just to clarify, you are talking about Zoom Events, not meetings or webinars, correct?