Trying to limit field access throuhg workflow

[Guido1982]

I'm trying to limit access to a dropdown through a workflow. I've setup the workflow so that it checks for the status I don't want changed by unauthorized people first. So " if status is 'do not change' " triggers a task. That task then checks against the role of the last user that last modified (so the person that just modified the status) and if the role is not the desired one I set the status back to 'do not change'. But no luck. Is this even possible?