In a perfect world, your jobs would be finalized when everything is said and done and the job is no longer going to change. In the real world, we know you sometimes need to make changes after a job has been finalized.
As long as payouts from a job have not been included in a payroll batch, a job can usually be unfinalized. If this option is available, you will see a button to "Unfinalize" on the Job Details page where the "Edit" button normally is.
Note: This feature is only available to Company Administrators.