Modifications are not allowed as that would alter the insurance and in the event of an accident it being invalid and the leasee liable for any loss to Mb.
Sure it’s in the agreement in some form or another. Not worth asking about imo as you do not own the car and they will not give permission so not worth asking..
Just tinting the windows would mean you modified the car and need to inform your insurance, if they did findout, they’d still allow you to have the policy until you try to claim then it will be sorry..