<xsl:template match="customer[office]">
  <office>
      office things
  </office>
<xsl:apply-templates select="*" />
</xsl:template>
</xsl:stylesheet>



That says that for a customer element with an office child,
output the fixed fragment 
 <office>
      office things
  </office>

then process all the child elements of customer.
It doesn't copy the customer element itself, or its attributes
and it applies templates to all child elements (including office)

David

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