(a) If it appears to the Commission that either an application, a statement in response or a statement in reply is not sufficiently definite and complete, the Commission may require a more definite and complete application, statement in response or statement in reply, as the case may be, to be presented.

(b) Where substantial justice requires it, the Commission with the concurrence of at least four Commissioners may allow the amendment of any application, statement in response, statement in reply and any document or exhibit which has been presented to the Commission.