CGST Rules amendment revises authority functions and omits specified rules, altering definitions and duties under the Act. The Fourth Amendment to the CGST Rules omits rule 122, rules 124 and 125, rule 134 and rule 137, revises rule 127 by substituting the marginal heading and converting duty language into an enumerated list of functions, and amends the Explanation after rule 137 to define 'Authority' as the Authority notified under sub-section (2) of section 171 of the Act, with the amendment taking effect from 1st December, 2022.