Amending Opening Balance figure in Bank Reconciliation screen should made an admin menu option

It is possible to amend the 'Opening balance' figure in the Cash Book Bank Reconciliation screen when reconciling transactions, but also by going into the screen, changing the figure and clicking on Reconcile. No warning message pops up to flag this as a potential problem, and so it can be done either accidently or deliberately. Our customer has asked whether it would be possible to have the Opening balance figure greyed out for all users, but having it as a Feature in System Administration so that it could be added to Admin or Manager roles only.