Part of me doubts that they will consider this to be a warranty service, because there is functionally nothing wrong with the older style sear, etc.
I think the updates were to address a common customer complaint, but the gun is not unsafe otherwise.
If they did offer a freebie, it would be out of the kindness of their hearts.

However, last year I sent my M&P40 FS in for repair, and they replaced the sear while they had the gun.

Your best bet would be to call them & ask.
1 (800) 331-0852