Alter Advanced Custom Field rendering in admin

functions::custom_field_render.php

<?php
/*
 * This snippet is from a project where I used an ACF Options gallery field to collect a set of icons.
 * This fields data was then used to replace a radio field's options with the actual icons.
 */
class Special_Excerpt_Icon {
  function __construct() {
    // filter load_field on all 'radio' fields
    add_filter('acf/load_field/type=radio', array($this, 'on_acf_load_radio_field' ) );
  }

  /**
   * Replaces this fields options data with the overview icons
   * set in the site options' icon gallery
   * @param  array $field the field settings array
   * @return array        The modified field settings array
   */
  public function on_acf_load_radio_field( $field ) {
    // bail out if not requested within the admin
    if (! is_admin() ) {
      return $field;
    }
    // check against the exact field we intend to modify
    if ( 'field_588c095495cb5' === $field['key'] && 'group_586bf7cc49163' === $field['parent'] ) {
      // init the field's 'choices' prop
      $field['choices'] = array();
      $icons = get_field('overview_icons', 'options');
      if($icons) {
        // use ACF's native 'choices' structure
        foreach ($icons as $icon) {
          $field['choices'][$icon['id']] = '<img class="excerpt-icon" src="' . $icon['sizes']['thumbnail'] . '">';
        }
      }
    }
    return $field;
  }
}