I was in the same situation your are a 2 months ago. When I was in the showroom I listened to the stock 6 cd changer system and said no mods because it sounded okay and I too planned to lease. My wife even asked me if I was going to swap out the deck because that has always been my practice for every new vehicle purchase. I definated responded no......no mods on a leased vehicle. Within a few days I was becoming unhappy
with the stock stuff and decided on a change. I installed a Alpine 7894 in the process of changing my fronts, will leave my rears stock for fill and adding amp and sub. All these mods will have no cutting or drilling. My deck looks great and fits very nice with the Nissan pocket. The only problem is amp location and sub enclosure that will not take the entire space in the hatch area. Wish JL stealth box was available. When installing make sure who ever does it leaves all the stock wiring in place and does not hack it up.
Ask them to put connector on the wire they do cut so that if you return your X that all the stock equipment can be re-install without too much problems. Also talk to the lease company and ask them what is expected when it is returned. I was told that the stock deck was required to be in place.