modifying XalanDocument nodes

I'm trying to read an XML document, find and modify some elements, and write it 
again as XML.  This worked OK using just Xerces, but then I was inspired to try 
XPath searches with Xalan-c, and I'm perplexed.  I can wrap a Xerces doc in a 
XalanDocument, and do the XPath search, but then I can't modify the 
XalanDocument.  Since the search returns XalanDocument references, I can't 
modify the original Xerces doc either.

Is there any way to make Xalan-c support editing a document this way, or am I 
barking up the wrong tree?  I've already tried using 
XercesDOMWrapperParsedSource(), but (as mentioned) I can't modify the wrapped 
document.  Would I be better off with Pathan?

Thanks,

George