You have to add an annotation or a note, and choose in the options (properties of the note) "link to the room" and not "linked to the current configuration".
It doesn't seem possible. The configuration property takes over the ownership of the file. A 3rd configuration is required, or a property with a different name.
I also think that you need to add a configuration, Lucas I don't have the option "link to the room" I use SLD 2012 the only place I have options is in the property manager in "Format text" the button Link to property" see screenshot
EDIT
Lucas is right, after selecting the note in the property manager, in "Text format" click on the "Link to property" button, then check "Component to which the annotation is attached" and choose the desired property.
I was a bit hasty in my answer, indeed with the above method we display the property of the drawing (which can be different from that of the model)
My goal was to display the model property of the "Customize" tab, which is not possible if you have the same property in the "Configuration Specific" tab.