big changes while incubating can cause the eggs to go bad. when you make changes durning incubation, it needs to be small changes. if the humidity is low and your eggs dimple, you panic and slam the eggs with high humidity, you're taking a big chance in losing eggs.

vpi did some test while incubating eggs in different conditions. then they change half the eggs to the other condition. the ones that started off and stayed in the same condition though out incubation did fine. but the ones they changed not so good.