Is it possible to create and use some lookup table to replace (for instance) %u in mail_location?

Suppose my mail_location is:

mail_location = maildir:/private/var/mail/nl.rna.mail/%u

But I would like to use a simple lookup table to replace %u with another value, say '8DB4E345-9144-4F92-8C9F-9D47BB61CBF8’ instead of ‘username’. Is there a (simple) way to do this?

Gerben Wierda Chess and the Art of Enterprise Architecture <http://enterprisechess.com/> Mastering ArchiMate <http://masteringarchimate.com/> Architecture for Real Enterprises <https://www.infoworld.com/blog/architecture-for-real-enterprises/> at InfoWorld On Slippery Ice <https://eapj.org/on-slippery-ice/> at EAPJ