I can leave my old stylesheet alone and do the following:

<xsl:import href="syllabus.xsl"/>

<xsl:template match="pamphlet">
<p><xsl:apply-templates/></p>
</xsl:template>

<xsl:template match="article">
<p><xsl:apply-templates/></p>
</xsl:template>

This will merge two stylesheet rules so that the importing styleesheet's rules have precedence over the other.

Transformation example: recommended-base.xsl recommended.xsl

Input documents: books-1.xml books-2.xml