> Therefore my question: Is there any way of changing the
> standard external.gif in the Win version of HTTrack?
Err, not really (except by overwriting the current 
external.gif file) ; you can either rewrite links as 
external (http://..) images, or rewrite them as 'blank' 
images (external.gif) ; but not yet 'choose' which image 
should replace the missing one..