Given, however I typically do not edit Labels in this manner, it's no concern of mine. However it can be done.
As any text overrides that I may make to a C3D label are few I still use the Ribbon or Rt-Click operation.
further, given that I still do a lot of training I do not 'customize' C3D, and try to find the must productive methods from the boxed product.
Conversely, I started out on vanilla AutoCAD, then Land Desktop, then Civil 3D, and I've used the shortcut "ET" on them all for almost 20 years, so like the OP's request, we have an ET command that edits Civil 3D labels, text, mtext, ArcAlignedText, etc.
Thankfully, Autodesk allows us various ways to do many things.
Correct however
most if not all NEW users to C3D do not need the confusion of seeing customized commands or functions
during their training sessions. So I would be doing them no favour to have MY installation of C3D customized to any degree
during a training class.
Yes it is fantastic that we can customize and build commands to suit our needs! Again, must don't need to be confused by
seeing commands or function that they will not have access to, right Out of the Box.
And along those lines, this is where I also disagree with most 'implementation' plans that include the establishment of
a 'templates' prior to training. As for me it is imperative that the users ALL know the how and why of Styles creation, and feature settings. But not teaching them these things does them a disservice in the long run.