As I understand it, if your current job description accurately reflects what you do, then there is no need to do a new one. If you do have to review it, then the new one should reflect what you do. It should be agreed between you and your line manager.
Changes to hours (other than those outlined in AfC), introduction of shift patterns etc are changes to contract terms and should be treated/negotiated separately. Any changes would have to be negotiated with the unions as the Staff side representative (even if your not a member). The end result may be the same, but at least due process would have been followed.
