Currently to change a revenue schedule, Puzzle needs to cancel and stop the existing one schedule on the back-end, and manually re-create the new schedule for you. We are working on creating the option to cancel/pause existing schedules and will let you know when that is ready.
In situations where the user does not want to change what is in Stripe - if the user need to modify and resend an invoice in Stripe, that change will be reflected in Puzzle.