Assertion (A) is true; the 42nd Constitutional Amendment Act, 1976, is widely referred to as the 'Mini-Constitution' due to the extensive and significant changes it introduced across various parts of the Constitution. Reason (R) is also true; the amendment indeed made substantial changes, including to the Preamble (adding 'Socialist', 'Secular', 'Integrity'), the Seventh Schedule (shifting subjects from State to Concurrent List), and affecting a large number of articles (more than 50).