You can prohibit updates to the plan dates of a workpack by using the Freeze Plan Dates command. Right-click a workpack in the List View and select Freeze Plan Dates from the shortcut menu to freeze the plan dates of a workpack. When the plan dates of a workpack are frozen, they are set to read-only, and users cannot change the plan dates when they update progress for the deliverables.
To allow plan date updates to the deliverables of a workpack that has been frozen, right-click a workpack with read-only dates in the List View and select Unfreeze Plan Dates.