For the service doc, you could use the <documentation tag for that like https://github.com/geonetwork/core-geonetwork/blob/develop/web/src/main/webapp/WEB-INF/config/config-service-admin-csw.xml#L5. It will be use by the doc module to create the service documentation https://github.com/geonetwork/core-geonetwork/blob/develop/web-ui-docs/generate-jeeves-services-doc.xsl.