If you choose to make it read-only in my facility preventing me from having the ability to recover from a fault, be prepared to pay for my lost production. Either that or commit to being on-site with in 1/2 hour of a phone call to you throughout the warranty period.
Two days ago, our facility experienced a component failure in a new control system. Had the code been locked like you suggest, the builder (2 states and no less than hours away) could easily have found himself fighting a lawsuit today. Because I had ability to get in and make the necessary changes to the code, our downtime was kept to a minimum.
I understand that OEMs and programmers need to protect themselves, but there is a line. Locking out the code or setting passwords for anything other than honest-to-god safety reasons is, IMHO, crossing that line. Hard-copies, CDs with original code, and contractual agreements are the right kinds of solutions here. I strongly suggest staying away from the lock-out method.
Steve