register_meta('post', 'idToPreserve', array(
      'type'         => 'integer',
      'description'  => 'Id to save to the db',
      'single'       => true,
      'show_in_rest' => true
    ));

register_meta('post', 'idToDiscard', array(
      'type'         => 'integer',
      'description'  => 'Id we use only temporarily.',
      'single'       => true,
      'show_in_rest' => true
    ));

add_action('added_post_meta', 'doThing', 10, 4 );

public static function doThing($meta_id, $object_id, $meta_key, $_meta_value) {
  if ($meta_key !== 'idToDiscard) return;
  //Do Things
}

public static function remove_custom_meta($post, $data, $update) {
  return delete_post_meta($post->ID, 'idToDiscard');
}