Hi Deven,
My suggestion would be as below
1. Create a delivery block reason Z1 by copying 01 : Credit Limit. (I hope you are aware that delivery reason definition has a column CONF which controls wheatear to confirm quantity or not )
2. Assign this delivery block in sales order type (VOV8) so that system will set delivery block Z1 in sales order header.
3. Whenever sales order need to be confirmed, authorized person can remove delivery block by going in to VA14L
4. Once Delivery block is removed system will confirm qty in schedule line subject to stock available.
Hope this would be helpful....
ATP