I have two branches for different versions - one for current development and another is long-time support several years old. As a consequence they differ significantly. I ha
Remembered, where I have seen something similar. It was here. Linked script helps as well.
With the script you might do it with one-liner:
$ git merge-associate Old/Path/Original.txt :1:New/Path/Renamed.txt :3:New/Path/Renamed.txt
Same as if git merge-file supported :stage:filepath syntax without doing all the fuss around git show :1:New/Path/Renamed.txt > 1.txt; git show :3:New/Path/Renamed.txt > 3.txt described in Git FAQ.