Hi,
No, clients are not authorized to change the order status. Only an administrator access level can change the order of status manually through back-end.
For instance, the situation is also the same for PayPal.
Firstly, the order will become "pending", the shopper will be redirected to PayPal payment screen. If the shopper pays the amount, PayPal sends API call to your Virtuemart Backend (in the background). This API call simple says: "The money has been received". So your Virtuemart will change the order status from "Pending" to "Confirmed" automatically.
But that kind of thing can't be possible with Bank Deposit. Your Virtuemart must communicate with the Bank with API calls to update the "order of status", which is impossible. No Bank would do that. The status will remain being "pending" until an administrator manually changes it to "Confirmed".
Regards.