Fastest way to find pattern in XML Node

I have an XML file which contains some Nodes that needs to be varied at runtime. For example:

<pt:Type>#type</pt:Type>
<pt:Value>#value</pt:Value>

I'd like to scan the XML file and search for Nodes which have a "#" pattern in it. My purpose is to fill up the XML using some data I have in memory. Which is the fastest way to do it in Java ? Maybe is there an XPath expression to gather all nodes having a certain value ?

Thanks!