[modeller_usage] Editing pdb file for a multimer

I plan to model a homomultimer by modeling separately each chain and then combining the results. To this concern, are python scripts available for (a) inserting the chain label at position 22 (which was not inserted the way I did), (b) renumbering the atom serial number, TER inclusive? I understand I have to learn seriously how to program with python. Thanks francesco pietra