For many aspects of a document's appearance, you can control the behavior of the stylesheets by changing parameters.
<xsl:param name="double.sided" select="1"/>
<xsl:param name="page.margin.inner">
<xsl:choose>
<xsl:when test="$double.sided != 0">1.25in</xsl:when>
<xsl:otherwise>1in</xsl:otherwise>
</xsl:choose>
</xsl:param>
<xsl:param name="page.margin.outer">
<xsl:choose>
<xsl:when test="$double.sided != 0">0.75in</xsl:when>
<xsl:otherwise>1in</xsl:otherwise>
</xsl:choose>
</xsl:param>The parameters are described in the documentation that comes with the distribution.