A schedule change can happen on every flight.
Yes, my last schedule change was also on DPS-IST (21:00 to 21:05) but that's a coincidence.
TK is requesting acceptance or denial in case of a schedule change and my understanding is that the itinerary is in some sort of pending state until the decision is made.
Yes, you have the right to deny as you have the right to cancel the booking in that case.
The purpose of my post was to find out if the online process is working for you or not. In my case, the online acceptance never worked and I always had to call in.