I'm really not qualified to weigh in on this. I imagine the timing of the airbags is different in the new seats, which could cause them to deploy too slowly or too quickly in an accident if the RCM wasn't programmed. Also, I suspect the door panel tethers prevent the panels from coming off when the seat airbags deploy (likely striking the door in the process), without which, you could have the panel strike a passenger. The resulting injury could vary from minor to deadly, depending on a bunch of factors. I could't possibly contemplate the number of ways these panels could cause injury, but it seems like cheap insurance. Finally, I would think you would have the matter of future resale value and liability to a subsequent owner to consider. At the least, I'd think you'd want to have a buyer acknowledge that they are aware that you have not performed all the safety upgrades when you retrofitted the seats, which would likely affect the resale value. I'm not an attorney, and wouldn't presume to offer legal advice, but it seems like you'd want to disclose something like that to a buyer. For the minimal effort and your own safety, I'd take the extra steps to do the safety upgrades. Good luck!