Selected a number of files
set creation time - tagged and added new -date- only (leaving time untagged)
tagged set last modified time - copy from created
noticed that 'last accessed' time is applied on all files.
actually, this wasn't the idea.
Q: how to leave the time unchanged in this scenario?
Vainly tried to undo this (ctrl-z).
What was the Created timestamp before making the change?
We can't see that detail, but it is often the same as the last accessed timestamp (since Windows no longer updates the last accessed timestamp after the file is created, by default).
If the Created timestamp was the same as the Accessed timestamp before making the change then what happened is the expected behavior: The date part of the Created timestamp was changed, and then the Created timestamp (date and time) was copied to the Modified timestamp.