As of now, once one assigns a workflow scheme to a project, it's not possible to change the Workflow and the steps any more. While the reasons behind this are clear, this is a too restrictive limitation. If modification to workflows which have been assigned to active projects are not in conflict with what's been assigned, administrators should be able to change things like steps descriptions. More importantly, administrators should be able to add a transition to a step or even a step, if these information are not in conflict with what's been already assigned. I'd add that, should these information be in conflict, a screen on how to resolve conflicts would be all that's required.