Attached is a patch that I think will work.  I have not tested it because I do not know how to make my home directory, and only my home directory, read-only.

Brian, how did you do it?  I now have Win 10.

When I rt click user/terry and select properties, there is a tri-state box "[ ] Read-only (Only applies to files in folder)".  It initially has a solid square, and changes to blank and checkmark.  Try to apply, there is an unselectable grayed-out choice to apply to the directory only and a mandatory choice to also apply recursively to all files and subdirectories.  I am loath to do this since there are 47000 files (40000 in appdate, which seems grossly excessive, but that is the report)

I would like this tested anyway at least once on linux and mac.  Testing procedure: change name of .idlerc, lock home dir, run installed IDLE from command line.  Should exit with message.  Run patched repository IDLE.  Should run, reporting temp dir and deleting it on exit.  (Unlock home dir and rename .idlerc back).