You can load and process the file using
<xsl:apply-templates select="document('crap.xml')" mode="crap"/>
and then include another stylesheet module containing mode="crap" template rules using <xsl:include href="crap.xsl"/>. You don't have to process different documents using different modes or different stylesheet modules, but it can avoid confusion.
Michael Kay
http://www.saxonica.com/
Author, XSLT Programmer's Reference and XPath 2.0 Programmer's Reference