You've got the general idea. But the only template you need in addition to the identity template, I think, is
<xsl:template match = "property[@name='url']/value">
<value>jdbc:mysql://localhost/devDB</value>
</xsl:template>
Alternatively, you could probably just delete the
<xsl:apply-templates select="*"/>
from your template rule, because it's this instruction that's causing the old value element to be copied.
Michael Kay
http://www.saxonica.com/
Author, XSLT Programmer's Reference and XPath 2.0 Programmer's Reference