Can I edit a request after it's been approved?
By default, if you can approve a request you can also change it's status back to unapproved and then edit it or pass it back to the original requester to edit it. But the system doesn't let you individuals edit their own requests after managers have approved them.
Completed / Taken requests
By default, Turbine doesn't let anyone edit a completed or taken request. Instead, you can clone the request and then delete the completed original.