You're welcome, August
The thoughts I had writing out these Infos to you were somewhat like "maybe he doesn't know that ? Well, for the things he want to do it seems to be better if he knows that.. - Sometimes it is better to have more Infos..."
And I am very grateful that my long notes will be helpful for you in some cases - but not only for you - for every one who will come to this thread in the future.
Since Dan posted about his KMET Macros, I knew I forgot something ... but that only shows that I am a human 
For this thought you have - here is an additional thought that I have vor you:
- there is also this Macro from Dan - which I use quite often - Go To Group by Name.
- I would use it as a starting point and add additional functionallity to it with a custom Button named "Options".
- Pressing that button could throw a Prompt where I then could disable the Group and choose between Editing as XML or JSON using KMET with a predefined String like "edited with KMET &
todays date" which then can be added to the Group Name String in the XML or JSON in BBEdit.
Something to know here: Since the Macro returns the Group UUID you would have to script the Disable Macro Group Action with either AppleScript or JXA.
The Next thing is that you would have to know how the Action is working if it uses Group Name and UUID then you need a custom List generated fron JSON so that you can parse both from your selection.
I think this quite a nice approach - because of that I think I'll do this for my self....
That's all I have for now...
Greetings from Germany
Tobias