Are u talking bout an engine change on ur certified copy? Did the reciept u threw away was the chit that they gave u at the cashier in licencing office? If so, u can just wait abt a month to get the cert wit the new engine number. And if u need to get inspected before, jus tell the inspector that u now put in d engine an u want to inspect b4 u go on d road, u may need the reciept of purchase for the engine for this. If not, ul have to go back to licence office an pay again.