What is the ruling of Islamic law regarding renting a sum of hard currency for a sum of local currency, due to need?

It is unanimously agreed that the leasing of current money is invalid because it is not possible to benefit from it while its physical form remains, which is a fundamental condition for the validity of a lease. What you did is, in reality, a loan of the amount, because you returned its equivalent, not its physical form. If the return was more than the original amount, then it is a forbidden usurious loan. As for the old dirhams and dinars, scholars differed on the permissibility of leasing them for adornment. The Hanbalis permitted it, while the majority prohibited it. Everyone agreed on the invalidity of leasing them for purposes other than adornment, in which case they transform into a loan.