Event linkage is a transportable object, thus there is no way to simply 'switch off' a workflow. Simply switching off a Workflow may even have legal implications since Workflow provides an important audit function, and being able to disable it defeats that purpose. All is not lost however: If you have a workflow that requires this feature, you could include a start condition that always fails and only enable it when you want to disable the workflow.

We developed a Z transaction that updates SWETYPV. Let me know if you are interested in this tool and I'll post it here too.