code: def modify_metadata(identifier, metadata,
                      target=None,
                      append=None,
                      append_list=None,
                      priority=None,
                      access_key=None,
                      secret_key=None,
                      debug=None,
                      request_kwargs=None,
                      **get_item_kwargs):
      
      item = get_item(identifier, **get_item_kwargs)
      return item.modify_metadata(metadata,
                                  target=target,
                                  append=append,
                                  append_list=append_list,
                                  priority=priority,
                                  access_key=access_key,
                                  secret_key=secret_key,
                                  debug=debug,
                                  request_kwargs=request_kwargs)
docs: Modify the metadata of an existing item on Archive.org.
  
      :type identifier: str
      :param identifier: The globally unique Archive.org identifier for a given item.
  
      :type metadata: dict
      :param metadata: Metadata used to update the item.
  
      :type target: str
      :param target: (optional) The metadata target to update. Defaults to `metadata`.
  
      :type append: bool
      :param append: (optional) set to True to append metadata values to current values
                     rather than replacing. Defaults to ``False``.
  
      :type append_list: bool
      :param append_list: (optional) Append values to an existing multi-value
                          metadata field. No duplicate values will be added.
  
      :type priority: int
      :param priority: (optional) Set task priority.
  
      :type access_key: str
      :param access_key: (optional) IA-S3 access_key to use when making the given request.
  
      :type secret_key: str
      :param secret_key: (optional) IA-S3 secret_key to use when making the given request.
  
      :type debug: bool
      :param debug: (optional) set to True to return a :class:`requests.Request <Request>`
                    object instead of sending request. Defaults to ``False``.
  
      :param \*\*get_item_kwargs: (optional) Arguments that ``get_item`` takes.
  
      :returns: :class:`requests.Response` object or :class:`requests.Request` object if
                debug is ``True``.