Is it permissible for me to demand a reduction in the price of the property after I have agreed to register another property of lower value, in the event that the seller only accepts the old price?

If a property is purchased and an option period is specified and then expires, the property belongs to the buyer. The seller has no right to retract or exchange it for another property. If the seller does so, the buyer has the option to either agree to the substitute property or refer the matter to a judge.

If the buyer accepts the second property due to insufficient evidence, he is not entitled to litigate the matter thereafter. However, there is no harm in negotiating with the seller to request a price reduction after the agreement, while making it clear that the seller's action was wrong and unjust.