Yes, you can change schedules for active sequences. To change the schedule for any sequence:
Open the list of your sequences by clicking on the Sequences page.
Select the sequence in which you want to change the schedule by clicking on it.
Open the Steps tab of the sequence interface.
Click on the Sending schedule button in the upper right corner to select a new schedule from the drop-down list/customize the existing one:
Note: you must first create an alternate schedule to be able to select a new sequence schedule. To do this, navigate to the Schedules page of the Settings tab and click Create new schedule.