code: def change_meta(self, para, new_value, log=True):
          
          if not new_value:
              return
          para = para.lower()
          if para == 'history':
              raise ValueError(
                  'History can only be extended - use method "note"')
          old_value = self._content.get(para, None)
          if new_value == old_value:
              return
          self._content[para] = new_value
          if old_value and log:
              self._add_history(entry_type="METADATA_CHANGE",
                                entry='Changed parameter "{para}" '
                                      'from "{old}" to "{new}"'.format(
                                          para=para,
                                          old=old_value,
                                          new=new_value))
docs: Changes the meta data
  
          This function does nothing if None is passed as new_value.
          To set a certain value to None pass the str 'None'
  
          Parameters
          ----------
          para: str
              Meta data entry to change
  
          new_value: str
              New value
  
          log: boolean, optional
              If True (default) records the meta data change
              in the history