xslt replace value based on a match from an imported nodeset

I'm attempting to import a node set and then search the input stream and do a replace on a match of a value.

<xsl:variable name="root" select="/"/>
<xsl:variable name="myNodeSet" select="collection('file:/C:/temp/?select=*.xml;recurse=yes')"/>

<xsl:template match="node()|@*">
    <xsl:copy>
        <xsl:apply-templates select="node()|@*"/>
    </xsl:copy>
</xsl:template>

<xsl:template match="someElement/@name">
    <xsl:attribute name="name">
        <xsl:if test=".=$myNodeSet//matchName">
<!-- here is where I'm trying to replace someElement/@name with a sibling attribute value -->
<!-- of the matched node in the if test -->
           <xsl:value-of select="$entities/preferredAbbreviation[text()=.]/../Entity/@name"/>
        </xsl:if>
    </xsl:attribute>                                
</xsl:template>

unfortunately, it doesn't seem to work and I'm sure it has something to do with attempts to reference the test match of the if statement. should I be using a for-each instead here?

thanks a bunch.