> After I have mirrored a site, if I go back with
> slightly different settings, does this update those
> files already mirrored or only the new ones?> 
> As an example, if I changed the web browser info,
> would that change the html mirror files that
> WinHTtrack has already built?
Changing the browser ID might change what the site sends.  Local files are
changed only during an update and the site is different than local.

You can always delete the html files, that way you'll force a get of all html
files and not redownload all the larger image/video ones.