XML => XML : Changing some attributes

hello
I 'd like to write an xslt file that works on an xml file and writes 
another xml file
This xslt file is more or less an identity transformation.
   <xsl:template match=" * | @* ">
       <xsl:copy>
           <xsl:apply-templates select=" * | @* "/>
       </xsl:copy>
   </xsl:template>

But for some attributes , i'd like to change their values
<foo bar="xxx" /> ===> <foo bar="yyy"/>


XSL-List info and archive:  http://www.mulberrytech.com/xsl/xsl-list