XSLT For-each to display in a semicolon-delimited value instead of separate tags
Solution 1:
In XSLT 2 and later you can use
<LeadActor>
<xsl:value-of select="/StringAssetInfoMulti[attrTagName='LeadActor']/values/s" separator=";"/>
</LeadActor>
In XSLT 1 it is kind of obvious that you need to use for-each or apply-templates processing and then output the ; as a separator with <xsl:text>;</xsl:text> for either all but the last or all but the first item e.g.
<xsl:for-each select="/StringAssetInfoMulti[attrTagName='LeadActor']/values/s">
<xsl:if test="position() > 1">
<xsl:text>;</xsl:text>
</xsl:if>
<xsl:value-of select="."/>
</xsl:for-each>