code: def rename_db_ref(stmts_in, ns_from, ns_to, **kwargs):
      
      logger.info('Remapping "%s" to "%s" in db_refs on %d statements...' %
                  (ns_from, ns_to, len(stmts_in)))
      stmts_out = [deepcopy(st) for st in stmts_in]
      for stmt in stmts_out:
          for agent in stmt.agent_list():
              if agent is not None and ns_from in agent.db_refs:
                  agent.db_refs[ns_to] = agent.db_refs.pop(ns_from)
      dump_pkl = kwargs.get('save')
      if dump_pkl:
          dump_statements(stmts_out, dump_pkl)
      return stmts_out
docs: Rename an entry in the db_refs of each Agent.
  
      This is particularly useful when old Statements in pickle files
      need to be updated after a namespace was changed such as
      'BE' to 'FPLX'.
  
      Parameters
      ----------
      stmts_in : list[indra.statements.Statement]
          A list of statements whose Agents' db_refs need to be changed
      ns_from : str
          The namespace identifier to replace
      ns_to : str
          The namespace identifier to replace to
      save : Optional[str]
          The name of a pickle file to save the results (stmts_out) into.
  
      Returns
      -------
      stmts_out : list[indra.statements.Statement]
          A list of Statements with Agents' db_refs changed.