I wrote customer support about the fact that i would like to be able to turn it off permanently, here is the answer...
Hello Antoine,
Thank you for reaching out to Tesla. I am sorry for the delay in responding to your email.
I understand your concern as the lane departure currently can only be used properly in certain situations (on the freeway). On surface streets or streets not painted consistently it can cause a problem.
I will submit this as feature request, but my thinking is the place in which this feature sits as far as our future with FSD it is seen as a safety feature. Much like seatbelts, airbags, and emergency braking. Except, it has a lot of work to be put in that position.
If you imagine it working as it should there should be no reason to have to turn it off and would want something you want always on.
I hope this helps you understand our vision with this feature and why it re-enables itself.
We thank you for helping Tesla to accelerate the worlds transition to sustainable energy.
Alex G | Tesla Support
12832 Frontrunner Blvd., Draper, UT 84020
www.tesla.com/support