@johnnydecimal the groupedThings definitely needs to be copied and pasted back in too because that is where the IDs like 11.01 are saved.
In any case, your method works, which I am grateful for and want to thank you for.
The only thing is that one has to remember to make those copies before and/or after making changes. And, when one has to remember to do something, there is always a risk, not a small one, that one forgets. And changes cannot be undone, AFAIK. This is not a criticism, just a caveat for those using @ekafyi’s app.