revisionism

Concise Oxford English Dictionary © 2008 Oxford University Press:
revisionism/rɪˈvɪʒənɪzəm/

▶noun often derogatory

• 1 a policy of revision or modification, especially of Marxism on evolutionary socialist or pluralist principles.

• 2 the theory or practice of revising one's attitude to something.

– derivatives
revisionist noun & adjective.