This was one of the OOPSLA / Camp Smalltalk 3 fixes.

>From the preamble:

Change Set:		CS3-ImageOverwrite
Date:			3 November 2000
Author:			Michael Hewner, Doug Way, Camp Smalltalk 3 @ OOPSLA

Fixes a problem where if you tried to do a 'save as...' over an existing
image, an error notifier appeared.  This enhances things so that a
confirmation pop-up appears asking if you're sure you want to overwrite,
which you can say Yes or No to.  (This ended up involving a fair amount
of work, including adding a force-copy operation to FileDirectory, and
some refactoring was done along with this.)
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