Add code to custom taxonomy meta boxes

Custom-Taxonomy-Meta-Box.php

<?php
register_taxonomy( 'acme_custom_taxonomy', array( 'my_cpt', 'post' ), array(
  'meta_box_cb'	=> 'acme_metabox_cb',
) );

function acme_metabox_cb( $post, $box ){
	
  // Render the default hierarchical meta box form
  post_categories_meta_box( $post, $box );

  // Add all of our new stuff!
  echo "<p>This will show up below the checkboxes that you are used to!</p>";

}