Is it permissible to substitute the type of cargo specified in the contract?

Primary text

If the owner of the animal (lessor) stipulated a specific type of cargo, and the hirer (lessee) wishes to load something else, the lessor cannot accept it because the hirer cannot demand what was not agreed upon. Similarly, if the lessor requests a change, and this change negates the specific purpose of the lessee—such as the need for speed (requiring horses or mules), or the need for a stable load (requiring camels for heavy or long journeys)—the substitution is not permitted because it nullifies the lessee's intent, analogous to a riding animal contract.