How to Use XSLT Extension Points from a Publishing Template
It is possible to declare a WebHelp XSLT-Import Extension Points in an Oxygen Publishing Template to override or add additional XSLT processing.
Example:
<publishing-template>
...
<webhelp>
...
<xslt>
<extension
id="com.oxygenxml.webhelp.xsl.createMainPage"
file="xsl/customMainPage.xsl"/>
</xslt>