<?php

function add_title_merge_tag( $output, $tag ) {
  if ( 'title' != $tag ) {
    return $output;
  }

  return "Title " . get_the_title( $post_id );
}
add_filter( 'af/merge_tags/resolve', 'add_title_merge_tag', 10, 2 );

function register_title_merge_tag( $tags, $form ) {
  $tags[] = array(
    'value' => 'title',
    'label' => "Title",
  );

  return $tags;
}
add_filter( 'af/merge_tags/custom', 'register_title_merge_tag', 10, 2 );