If you are using the Professional version of Microsoft Project, here is what you can do:
1. Create the tasks that "might" happen. 2. Link the tasks that "might" happen to tasks that are needed in the project. 3. Enter task Duration for the "might" happen tasks. 4. Assign resources to the "might" happen tasks. 5. Select all of the "might" happen tasks and then click the Inactivate button in the Task ribbon.
With the "might" happen tasks set to Inactive, they will not impact the project schedule. When a "might" happen task is actually needed in the project, you can select the task and then click the Inactivate button again to re-activate the task.
