Can I add a scenario for Lease Buyback Scheme of the Property? (i.e selling 50% of the property back to government)

You are not able to liquidate 50% of the property.

The liquidate function for property is always based on 100%. However, you can work around to achieve the same effect.

Follow the steps accordingly when creating a scenario :

1) Liquidate Property 

2) Add New Property based on 50% of the value of the liquidated Property

3) Decrease Cash by the value of the new Property