As of today, changing a plane flight plan and activating with a 3-day delay may result in a number of flight cancellations if the user doesn't pay attention to the already-booked flights.
As of today, when a flight is booked, it is regardless of the potential – existing – conflicting flights. My guess is that a reasonable default would be to automatically cancel a flight being booked if it conflicts with an already-booked in flight in the system for the same plane – maybe additionally taking transfer time into account if necessary.
IMO, this feature would be quite useful to avoid any unwanted flight cancellations, and to avoid time-consuming and error-prone micro-management when changing flight schedules. It is already partly implemented when activating a flight plan immediately on a new aircraft – automatically cancelling the flights conflicting with the transfer, so I guess this wouldn't be a too complex addition.