Is it permissible to convert a guarantee contract into a lease contract, where the car owner leases it to the worker for 200 Saudi Riyals per day? And is this solution considered a legitimate stratagem?

This stratagem is sound, and it is permissible for the car owner to rent out his car for work therein according to their agreement. The worker then owns the usufruct of the car for the agreed-upon period. This is based on what is established in the Two Sahihs, that the Prophet, peace and blessings be upon him, appointed a man over Khaybar, and he brought him fine dates (tamr janiyib). When the Prophet, peace and blessings be upon him, learned that this was by exchanging two sa's for one sa' of another kind, he commanded him to sell the mixed dates for dirhams, and then buy fine dates (janayib) with the dirhams. In another narration: "Do not do that. Rather, it should be like for like, or sell this and buy this with its price." This indicates that the stratagem to validate a contract is legislated, and it involves abandoning a forbidden contract and resorting to permissible contracts.