Limitation on reassessment powers: amendment bars reopening assessments or altering refunds for specified prior assessment years. The amendment inserts a proviso to section 14A that, with retrospective effect from the specified date, precludes the Assessing Officer from reassessing under the reassessment provision, from passing orders enhancing assessment or reducing refunds, and from otherwise increasing an assessee's liability under the statutory amendment procedure for assessment years beginning on or before the specified cutoff.