Multiple Clients / Working with Classes?

[mmmmh]

Maybe it is too obvious and I cannot see the wood for the trees, but I don’t know how to serve different layouts/content to two different clients.

I understand that assigning classes to individual modules in the settings is one way to differentiate what gets displayed, but how is the class determined on the client-side? I run MMM as server-only and plan to use two different Raspberry Pis to display its specific layout. Can I pass an identifying string with the URL? Or is running two separate instances from different directories the better way?