Is it possible to create multiple scenarios for one event?
Yes, you can. For example, when adding a new user, one scenario will assign a course, and another will send a notification to the manager.
Is it possible to restrict a scenario to only certain Users?
Yes, use filters (by company, department or job title).
Is it possible to disable the scenario without deleting it?
Yes. Uncheck the box."Active"— the script will be saved, but will not be executed.