I just want to clarify exactly what is being asked, are you looking for a native tabcmd that could be used to test permission sets prior to the automated email being sent out?
Not just permissions but also all other security settings like any sort of row level security (RLS).
For example, permissions just checks whether or not a report is allowed to be executed by a user. But even if a user has access to a report, it doesn't mean that they can see all the data in the underlying data set.
I am looking for a feature that checks at least the RLS at the minimum. I really don't care much about report permissions as I will probably maintain that manually in my tabcmd meta data, however, I won't have something that controls the data level security since Tableau runs that server side. So it has to be a server side API.