Property - government value is increased after booking plot at very initial stage. at the time of registration, how can it be shown in sale deed without paying the difference amount to the developer.

Say initial stage - booked property at 800 per sft goverment value. so 30*40 plot will cost 9,60,000. Registeration was as discussed planned in march 2018. But from last 6 months after booking plot. The government rate is not incrased to 1200 per sqft. So at the time of registration in march 2018, as it has to be registered at the value of government price in my case. How can this be shown in sale deed, because the value of property changed to 14,40,000. The difference amount is 4,80,000. As i dont have to pay developer this difference amount as per agreement made. How can i approach this problem. Because i dont want developer to show as difference amount paid by cash in sale deed. As i dont want any problem in future. kindly advice and guide in this scenario. Thanks in advance.