Replace search keywords (whole words)

add_filter( 'asp_query_args', 'asp_replace_search_keywords', 10, 2 );
function asp_replace_search_keywords( $args, $id ) {
  /**
   * Add as many words as you want. On the left side place the
   * word or words separated by comma to replace.
   * To the right side, place the single word to replace it with.
   */
  $replace = array(
    'word1' => 'word2',       // Replace 'word1' with 'word2'
    'word3, word4' => 'word5' // Replace 'word3' and 'word4' with 'word5'
  );
​
  // ----------------------------------------
  // Do not change anything below this line
  // ----------------------------------------
  foreach ( $replace as $k => $w ) {
    $kr = explode(',', $k);
    foreach ($kr as $krk => &$krv) {
      $krv = trim($krv);
      if ( $krv == '' ) {
        unset($kr[$krk]);
      } else {
        $krv = '/\b' . $krv . '\b/u';
      }
    }
    if ( count($krv) > 0 ) {
      $args['s'] = preg_replace($kr, $w, $args['s']);
    }
  }
  return $args;
}