You could consider using the Reschedule / Unassign Assignments dialog as a starting point. This dialog will allow you to enter a new Scheduled Start Date and apply from the List tab. Scheduled Finish really should be a calculated field based on adding duration. If work is long duration though and interruptible then Scheduled Start + duration isn't always Scheduled Finish.
I suspect you are trying to use Scheduled Finish as the Finish No Later Than date.
If you use this dialog as a starting point, you could have a script or escalation that changes work order status once the field is set.

