The buttons are not editable.
If you still have access to an earlier Word version you could create an
add-in with buttoms of your choice - see
http://www.gmayor.com/Toolbars_in_word_2007.htm

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Graham Mayor - Word MVP
My web site www.gmayor.com
Word MVP web site http://word.mvps.org
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> I would like to create a modified version of the "print" button to
> the Quick Access Toolbar in MS Word 2007 - where the modified button
> will trigger an macro that I set up to print to a different tray in
> my printer.
> What is the default location of these graphic files for the buttons,
> and can I use Photoshop, for example, to create a modified version?