Your topic title is "Flexible Level Marker (
Plan)" but it would seem that you're talking about level indicators in section/elevation. If this is indeed the case much, if not all, of what you ask for can be achieved with an object. The downside is that it will not associate to other elements so must be moved manually when building elements are modifed, but that's the case will all your other notes anyway and is a simple matter. The screenshot shows an object I made for this purpose. It has leading and trailing text but not the dual elevation you mention. If it's close to what you're looking for I'm happy to share it and you could modify it as needed.
Regards,
Geoff Briggs
DeForest Architects
Seattle, USA
AC26 INT, M1 Mac, OS 13.2.1
Yes, you read that correctly, we are in the US but use the INT version, because the libraries are better.