The Smartproperties tool gives much more freedom than the built-in property editor in Solidworks. By the way, what version are you working on? for Smartproperties input masks, it is possible to " concatenate " existing properties.
On the other hand, I'm not sure that changing the Designation of a configuration is very wise but it depends on the work environment, what are we talking about... of configured parts, configurations of parts within an assembly... configuration of assemblies? It lacks context...
Otherwise, out of spite, it is possible to run a macro from Smartproperties:
I don't really see the point of the macro (or the Smartproperties mask for that matter) ... why not concatenate the two data directly in the Excel table of the Room Family?