Works contract classification change applies to post-effective performance; composition scheme eligibility depends on prior service-tax payments. Classification of long-term contracts shifts to Works Contract for services performed after 01.06.2007. Eligibility for the composition scheme depends on having validly exercised the option before payment of service tax for the contract; prior payment under earlier taxable service heads before the scheme's effective date precludes use of the composition scheme, whereas absence of such prior payment allows opting after the scheme came into effect. Option, once exercised, applies to the entire contract and is irrevocable.