Handling moving contents from an AC.ID to another AC.ID

Imagine I have stuff that goes into 26.02 (files, emails, paper documents).
I have put 26.02 as a reference in my email subject lines, inside my files, tagged my documents.

Now for some reason, I need to move the whole contents of 26.02 into 78.45.
How do you handle this?

Obviously, it’s not possible (and usually not recommended) to modify emails, so the 26.02 sticks in them.
In LaTex-generated PDF files, I don’t want either to modify the document. I often need to keep the exact version that I sent to someone/some organisation.

One rule that seems necessary to avoid confusion is to keep the legacy 26.02 reserved, with a link to the new location of the contents (78.45) and the date of the move/refactoring.

I would be tempted to put a link from 78.45 to 26.02, or at least some info that says that the contents originated from 26.02 (so that if I’m looking for emails I know I also have to look for mails associated to 26.02.

How do you manage such situations?
This happens a lot when you are initially designing the structure of the JD system, but as time goes, sometimes, you learn how to better sort your stuff and have to move contents from one category to another one.
Do any of you have recommendations about refactoring inside an existing JD structure?

Yeah I think this is the winning strategy. Leave yourself a pointer. Because this will happen, no matter how well you design your system.

But this is why I recommend not jumping right in to a system. “Think on it for a few weeks” or something is what I wrote. Play with a mind map or sticky notes or just pencil and paper for a while until you’re confident that you’ve got it right.