Can skipping placebo week to start new pack cause a change in cycle?

Yes: It changes the hormone cycle and can either cause prolonged bleeding or delayed bleeding; you should take the placebo pills to keep the cycle on track.

Skip placebo: You won't have a period when you skip the placebo week and go right into a new pack. However, if you do this often, people can develop occasional breakthrough bleeding.

Yes: Pills like Seasonique have 84 consecutive days of hormone followed by 7 days of placebo. The timing of your withdraw bleed will be directly related to when you stop active pills, so that will cause a "change in cycle". Be aware that there is also a higher likelihood of breakthrough bleeding with extended use pills. Continue to use condoms, even if you are on the pill to prevent STDs.