Использование параметризированного template
<xsl:template name="setSeparator">
<xsl:param name="listLength" />
<xsl:if test="$listLength > 1 and ( position() < $listLength )">
<xsl:text>,</xsl:text>
<br />
<br />
</xsl:if>
</xsl:template>
<xsl:template match="/">
<td>
<xsl:for-each select="object/cause_credit_list/cause_credit">
<span class="aslink" onclick="MO.openMoInfo('MO_CONTRACT', '{clientcredit_id}');">
<xsl:value-of select="contractdate" />
<xsl:text>/ </xsl:text>
<xsl:value-of select="contractnum" />
</span>
<xsl:call-template name="setSeparator">
<xsl:with-param name="listLength" select="count(../cause_credit)"></xsl:with-param>
</xsl:call-template>
</xsl:for-each>
</td>
</xsl:template>