Thanks for your question. At the present moment (MIDI Designer 1.6.x) we do not do conditionals of any kind. We've discussed showing and hiding panels or controls based on values of supercontrols (although there's no concept of panels like that, as such, yet, either), and related stuff like your suggestion.
Your case is a pretty specific one, where the subcontrol already controls what you want -- so you don't need to use channel changers or anything like that -- but you merely want the label to change. Even so, until we do conditionals full-on in MD, this probably won't happen.
Using multiple knobs/slider and Named Ticks, you might be able to create a strange workaround, and it might be worth expermenting on that side. For instance, a Named Ticks supercontrol can control a Named Ticks subcontrol, whose sole function would be labelling this third control... This is just an initial idea for investigation.
Thanks for your question and your passion for MD!