Nobody is going to know when you return the lease. But when they do an inspection to CPO it or just resell it they will notice and will likely change it back to stock on their dime, or leave it as is and hope the new customer doesn't know. It's not necessarily a modification that will inhibit a danger to a new customer.
Typically a lease return, has a basic inspection, if any damage is done to the car you are by contract obligated to pay a difference.
As far as modifications go it depends. Most of the time they dont care cause it can be returned to stock.