The cutoffs should not be changed at all during a comp.
Statements like that make it very obvious that you haven't been a part of an organizing team.
Cutoffs at competitions should properly reflect the amount of time an event will take versus the amount of time willing to be used on a specific event. In ideal circumstances, the cutoffs would be perfect and would allow for perfect clarity between organizers and competitors.
However, this isn't always the case. Sometimes more people than expected show up. Sometimes someone promising to scramble breaks their hand before the competition. Sometimes organizers are too lenient and make unreasonable cutoffs. There are lots of ways to have cutoffs change during a competition.
While it's not ideal to change cutoffs, sometimes it has to happen to have the majority of the competition run as smoothly as possible. I had to drop cutoffs significantly during a competition I organized, and I felt bad about that. I really wanted everyone to be able to compete, but sometimes you have to sacrifice some people's solves to ensure that a majority of competitors get to compete. Yes this is biased for faster solvers, but that's how competitions work. Faster people are more likely to finish all their times.
Cutoffs
should be changed at competitions only when absolutely necessary. Competition organizers
should make lenient schedules with slightly stricter cutoffs, ensuring a high likelihood of running on time. However, what competitions
should be like and what competitions are actually like do not always overlap, and this causes cutoff changes.