works contract tax : Compound scheme

My client opted, after awarding the project, composit scheme (4% on T.O) by submitting Form 250.  At the middle of the project (Total Duration of the project : 9 Months.  50% of work completed during the last 4 months), he is intending to change from composit scheme to regular schme (12.5% tax & input tax credit availing).  Is it possible under the VAT act?