Validity of sale agreement post property registration

Is the sale agreement (or agreement to sell) a valid document in court after the property is registered? Say I put a clause in the sale agreement regarding the issuance of OC. Stating the OC has to be issued by the builder in 4 months from the time of registration of the property else a compensation of X amount has to be given to the purchaser. Say, even after 4 months, the builder hasn't issued the OC, Can I approach the court to take a legal action with the clause in Sale agreement? I heard once the property is registered the sale deed will come into picture and the sale agreement won't be a valid. Is the above true? If so, how can we make sure the builder keeps his promise (via legal document) after the property is registered. Thanks