This discussion clarifies the possibility of amending notices or complaints filed under Section 138 of the Negotiable Instruments Act for dishonoured cheques. While a legal demand notice itself cannot be amended, a rejoinder notice can rectify errors. Complaints, however, can be amended after filing, but only for curable defects and with caution, as per Supreme Court rulings like S.R. Sukumar vs. S. Sunaad Raghuram. Amendments that cause prejudice or fundamentally alter the complaint, especially after cognizance is taken, are generally not permitted.