Sure, take a look at the concat() and substring() functions.
<xsl:template match="start_date">
<xsl:value-of select="concat(substring(.,8,4), '/', substring(.,3,2), '/', substring(.,1,2))"/>
(Not sure from your example whether you want dd/mm/yyyy or mm/dd/yyyy)
Michael Kay
http://www.saxonica.com/
Author, XSLT Programmer's Reference and XPath 2.0 Programmer's Reference