This can be done, but you would need to use a macro. See, for example:
http://social.msdn.microsoft.com/For...x?forum=isvvba
http://www.tech-archive.net/Archive/.../msg00169.html
You'd need to take a similar approach, adding the code to a macro you use for printing the document. IIRC, in Word 2003, naming the macro 'FilePrint' will intercept the normal print processes to apply the changes, but in Word 2010 that doesn't work.