Is it permissible to substitute a wife's deferred dowry of gold with its equivalent in monetary value or a plot of land?

Deferred mahr (dowry) is a debt. If the deferred mahr is gold, then exchanging it for a piece of land is permissible. This is a sale, and it requires all the conditions for a valid sale. Immediate possession is not required, but the substitute must be present. As for exchanging it for a monetary value in cash (currency exchange), it is permissible on condition of immediate possession at the time of agreement. This is because exchanging gold for paper currencies requires immediate mutual possession, and delay is not permissible, based on the hadith (definition) of Ibn Umar: "There is no harm in you taking the price of your day, as long as you do not separate and there is something between you."