sdorn has a very valid point. you leased your car, i.e., it is not yours. then you think of everything that comes to mind about modifying a car that is not yours. naturally, the answer is NO. as for returning everything back to it's original state before returning your lease, well need you ask us for an opinion? you know the answer.
as for getting it serviced without problems, i'd ask my dealership service department. i've heard this question answered in many different ways, so it may be a very individual circumstance depending on who is working on your car.