So Saber added "option to disable beacon lights via functions menu". However the implentation is not done very well.
First of all, the beacon lights are ON by default, instead of OFF.
It doesnt save the "state" of the beacon lights either, as soon as you start the engine back up, the lights turn back on, even when you had them turned off when you stopped the engine.
Add a keybind, just as normal lights!
So, they should be OFF by default, they should a keybind and the ON/OFF state should be saved in your playsession and ideally also in between sessions when closing down the game.