Yes, you can bulk edit tasks on a project. On the project, you would click on the box on the left-hand side of each specific Task that needs to be edited (or you can edit all of the tasks at once by clicking on the top box).
At this point, once your tasks are selected, click the Edit button. From here, scroll down to where it says Planned Hours, check this field and then enter the revised Planned Hours, and then click on Save Changes.
Terry Hynd EBSCO Information Services