Given that it's relatively harmless to do something like

  for x in *
  do
    local y=$x:r
    # etc.
  done

It occurred to me that it should similarly be possible to do that with
"local -P" or "private", but without the appended patch that generates
a warning message and leaves $y unchanged without aborting the loop.

With the below it remains an error to try to change the type of a
private parameter (and that is an actual error rather than just a
warning, like most other typeset errors) but simply reassigning
something of the same type is allowed.