Manually force a set of attachments into the sitemap

I have read the documentation on sitemaps, and I can see that my sitemap is indexing attachments. This is fine, but it’s only indexing attachments that are attached to another page or post.

I only want to index attachments that meet certain criteria:

• They are only pdfs;
• They contain at least one value of a custom taxonomy (mediatopic or mediaformat);
• They have some content in the description.

Now, I can build a loop that will go through and grab all the media I want, and return an array of IDs, or whatever I would need. My question is how to get these into the sitemap.

It looks like I can add this filter:

add_filter( 'wpseo_xml_sitemap_img', '__return_false' );

And my interpretation of the docs is that this will remove images from the sitemap. But maybe it’s meant to disable all attachments? I’m not sure. Then, there’s this example, to index images:

function filter_wpseo_sitemap_urlimages( $images, $post_id ) { 
  array_push($images, 'https://www.example.com/wp-content/uploads/extra-image.jpg');
  return $images; 
}; 
add_filter( 'wpseo_sitemap_urlimages', 'filter_wpseo_sitemap_urlimages', 10, 2 );

This seems like it would index the file itself, and not the attachment page, which is what i’m trying to index. Also, the hook name implies it only pertains to images, but that might not be true.

If I can get a list of URLs to the attachment pages I want to index, then run through that loop and run array_push on each URL, will this then populate my attachments sitemap with the entries I want?