For now, you can use the "filter" function to create your own custom filter to extend any static or dynamic routes.

see doc: https://github.com/nuxt-community/sitemap-module/blob/master/README.md#filter

a simple example:

  sitemap: {
    filter: ({ routes }) =>
      routes.map(route => ({
        ...route,
        lastmodISO: new Date().toISOString(),
        priority: 1

      })),
  }