In the case of cooking oil, it is (I assume, didn't check) a trial and neither the engine nor the oil are certified for regular flight. Even if ao, it most likely would be the specific engine that would be recertified, not the cooking oil derived fuel.

AvGas is different, there it is not individual engines that get re certified for using lead free fuel (faster for each engine but impossible due to the agevand obsolescense of these old engines), so the fuel has to certified for all engines at the same time.