Under Section 20, the Central Government's power to exempt certain aircraft or persons from the Act's provisions may ALSO be exercised to direct that such provisions apply to them:

Section 20 grants the Central Government a DUAL power: it may EITHER exempt an aircraft/class of aircraft or person/class of persons from all or any provisions of the Act or rules, OR - as an alternative - direct that such provisions apply to them SUBJECT TO MODIFICATIONS specified in the notification, giving flexible, calibrated regulatory treatment rather than a binary exempt/non-exempt choice. This power is not restricted to re-registered foreign aircraft, agricultural crop-sprayers specifically, ICAO concurrence, or a fixed ninety-day sunset clause - the exemption or modified-application notification can be tailored broadly and can, in principle, remain in force indefinitely unless the Central Government itself limits its duration in the notification's own terms.