Sorry, that should have been acf/format_value filter. Looking at your other questions I will expand on it.
add_filter('acf/load_value/type=relationship', 'get_extra_post_data', 20, 3);
function get_extra_post_data($value, $post_id, $field) {
if (empty($value)) {
// no value to filter
return $value;
}
// this is needed because we will be working with excerpts
global $post;
foreach ($value as $post) {
$post->excerpt = get_post_excerpt();
$post->image = get_post_thumbnail();
} // end foreach post
// reset post data because we messed with the global
wp_reset_postdata()
return $value
}
