> If certain nodes in this extra information exist I want to replace the
> corresponding node in /root/xform/xforms:model/xforms:instance/page with
> them.

That much was clear, but that's what the code you posted (and my
suggested rewrite) both did, assuming they matched the input at all
(which still isn't clear)

http://www.mulberrytech.com/xsl/xsl-list/#posting says: 

    Well-composed questions frequently include a small XML sample, an
    XSLT stylesheet, the results received, and the result that was
    desired - all in miniature, to make it comprehensible to readers new
    to your problem. (It is also not uncommon to discover what a problem
    actually is in the process of reducing it to an illustrative
    version.)


David