I'm implementing my institution's PP templates -- like so many others. At our organisation we're often presenting classified stuff and we're supposed to include a slide with information about classification and remind people to take their electronics out of the room.
Ideally, the user shouldn't have to remember to include this slide by herself: If beamer is told that that the presentation contains classified information, then it should automatically insert this slide after the title page. For now, let's just assume there exists a boolean classified.
As a workaround, I could do it as a transition on the title page template. However, that would look very strange when printing.
It feels like this question is related to Theme with a different footline for the titlepage (in principle, insert some stuff before and after should be equivalent?), but I haven't been able to proceed.
There is no MWE, as I don't even know where to begin. As such, I'm happy to just get pointers in the right direction, and I'll make sure to post a working result at the end.

\deb\classified{\begin{frame}\frametitle{Classified} Get the damn phones out of this room \end{frame}}somewhere in the in the preamble/ external preamble/custom package/custom class, and then simply use\classifiedclassified information or do nothing for not classified material ? – Fran Jul 16 '19 at 08:51%\classifiedwhen needed. If you are thinking really in some more complex that pressDel(a mandatory switch, or include information in\maketitle, AI to determine when is classified (haha), etc.) you will have to be more specific about your needs. – Fran Jul 16 '19 at 10:00\usetheme[classification=nr]{institutiontheme}. Hence, having an extra\classifiedis -- information theoretically -- redundant information. (It's basically a question of over-the-top style. I principle, I want the user to be able to start with a completely blank document, and use only what he knows from vanilla Beamer. I might have to abandon that.) – Martin Strand Jul 16 '19 at 10:07