Add External Sitemap To Index
Our plugin creates sitemaps on the fly for the content within WordPress. In some cases, you may have sitemaps for other parts of your site that you want to add to our sitemap index. For this purpose, we introduced the
wpseo_sitemap_index filter. You will find an example of how to use the filter here.
The last mod date is hardcoded so it would not update automatically with this code. If you would like to update the last mod automatically we suggest developing on the plugin or hiring someone. We highly recommend checking out Code Poet for available freelance WordPress developers and Human Made for development & consultancy.