Find and replace terminal-node text - xslt-1.0

Question

I am using XSLT to convert an XML document to an HTML document. I am using a technical writing editor that has a WYSIWYG editor but I can access the XML it is ultimately based on.
I have recently added variables to assist with subsequent translations of interface text. Here is an example of how they appear within ordinary text:
<text styleclass="Body" translate="true">Under </text><var styleclass="Interface b"><%BACKGROUND%></var><text styleclass="Body" translate="true">, click on one of the predesigned backgrounds</text>
I have already added new declarations to my XSLT document dealing with the styleclass attributes:
<xsl:template match="var">
<xsl:choose>
<xsl:when test="#style='font-weight:bold;'">
<strong>
<xsl:apply-templates/>
</strong>
</xsl:when>
<xsl:when test="#styleclass='Interface'">
<span style="color:white; background-color: rgb(98, 98, 98);">
<xsl:apply-templates/>
</span>
</xsl:when>
<xsl:when test="#styleclass='Interface b'">
<span style="color: rgb(98, 98, 98); background-color: rgb(233, 180, 0);">
<xsl:apply-templates/>
</span>
</xsl:when>
<xsl:when test="#styleclass='Interface c'">
<span style="color: black; background-color: rgb(234, 235, 237);">
<xsl:apply-templates/>
</span>
</xsl:when>
<xsl:when test="#styleclass='Warning a'">
<span style="color:#e74c3c">
<xsl:apply-templates/>
</span>
</xsl:when>
<xsl:otherwise>
<xsl:apply-templates/>
</xsl:otherwise>
</xsl:choose>
</xsl:template>
But I also want to change the terminal-node text <%BACKGROUND%> to simply Background. (I have a spreadsheet with the variable names and user-facing interface text, so this question does not involve individually replacing upper case characters with lower case characters.)
I think there are two approaches:
Simultaneously transforming the attribute and content of a node. My attempts here have failed.
Selecting terminal-node text, but I think that the text tag may pose a problem here.
Thanks for any suggestions.