Just whatever you do make sure it can be reasonably undone for when you take it back. They do want it to have original equipment, however if you give it back with obvious upgrades (read: makes it worth more) I think they will be happy to accept it, but read my last sentence carefully. If they give you buckets and you bring it back with a bench you'll get charged the difference, if they're sharp enough to notice, that is. Just keep the OEM parts and switch them back, then sell the parts to mitigate the huge losses you will experience for spending money on a leased car. I'd barely touch it if it were me. I remember seeing a guy willing to trade expensive aftermarket rims straight up for the stock ones because of something like this; if he wasn't getting any money out of the deal then what does that say for the dealerships return requirements?