Rate of exchange for GST and input tax credit rules updated; export invoice and GSTR-3B filing procedures modified. Amendments revise valuation and procedural rules: Rule 34 fixes the rate of exchange-Customs Board rate for goods and accounting-principles rate for services; Rule 44 mandates separate calculation of input tax credit components and market-price estimation for stock inputs lacking invoices; Rule 46 prescribes export invoice endorsements and alternate recipient/delivery/destination particulars; Rule 61 allows FORM GSTR-3B filing where GSTR-1/2 deadlines are extended and directs electronic generation and reconciliation of FORM GSTR-3 Parts A and B.