This is very required functionality - usually project manager will add the whole WBS task hierarchy and the tasks to the project. it still should not show to all employee in timesheet. Project manager should have option to tell in WBS task level, which tasks are open for using. Now the only possibility is to put all tasks closed and then open the ones which will be using this moment.

Closing will also close the plan of the hours etc. - so it is not a good work around.

To put only active wbs tasks to the project WBS tasks is not also good work around, when system should support Project manager work and this should manually change and update in some other place to follow up with whole WBS hierarchy.

Status Not started is default status in the activity line and of course to change several task to specific status would be good function in the form to select required one to the in progress and to show in timesheet or in other activities. Select the required one to be completed or to other status. This is almost very necessary after the status In process start to work with activity lookup filter and when Not started is default value in the task.