Pass rehype/mark plugins and other options like jsxImportSource inside mdxBundlerOptions .

return docs({
  // other options
  mdxBundlerOptions: {
    mdxOptions: {
      jsxImportSource: 'preact',
      remarkPlugins: [
        /* add or change remark plugins*/
      ],
      rehypePlugins: [
        /* add or change rehype plugins*/
      ],
    },
  },
});