Is it permissible to give the monetary value of gold gifted to Allah, as money, after the money becomes available?

It is not permissible for someone who has given out wealth as an act of drawing closer to Allah to take it back, based on the hadith: "Indeed, the one who takes back his charity is like the one who takes back his vomit."

If the gold has already left your possession and become the property of the donee, then it is not permissible to revoke the charity, even by purchasing it back.

However, if it was merely an intention and the gold has not yet left your possession, then charity is not binding by intention, and it is permissible to give out its value.

As for someone who has set aside something to give in charity but then decides not to give it, it is recommended for him to proceed with it, though it is not obligatory.