[WordPress]

00-find-all-events.php

<?php

private function find_all_events( $event_id ) {

  global $wpdb;
  $events = $wpdb->get_results(
    $wpdb->prepare("
      SELECT ID, post_content
      FROM   $wpdb->posts
      WHERE  post_parent = '%d'
      AND    post_status = 'publish'
    ", $event_id),
    ARRAY_A
  );

  return $events;
}

01-update-future-events.php

<?php

public function update_future_events( $event_id ) {

  $events = $this->find_all_events( $event_id );

  $iteration = 1;
  foreach ( $events as $event ) {

    preg_match_all( '/(\d+)/', $anniversary['post_content'], $matches );

    $original_year = $matches[0];
    $original_year = intval( $original_year[0] );
    $new_year      = ( $original_year + $iteration );
    $iteration++;

    // See forth-coming gist.
  }
}

02-update-future-events.php

<?php

public function update_future_events( $event_id ) {

  $events = $this->find_all_events( $event_id );

  $iteration = 1;
  foreach ( $events as $event ) {

    // See previous gist.

    $event['post_content'] = str_ireplace( $original_year, $new_year, $event['post_content'] );
    wp_update_post(array(
      'ID'           => $event['ID'],
      'post_content' => $event['post_content'],
    ));
  }
}