Hello,
I don't think you can restrict the access on status value selected in status field, you can restrict the sales orders based on transaction types and sales organisation level even display/change also.
B_USERSTAT/B_USERST_T these object will use when you give create/changes for sales orders in WEBUI.
moreover you may not restrict all assignment blocks with authorisation objects in WEBUI, you need to restrict them by business role level, we can also restrict assignment blocks by activating suitable BADI's/component enhancement. technical abaper would help on this.
below are the authorisation objects will help you to restrict sales order. hope will help you. thanks
CRM_ORD_LP
CRM_ORD_OP
CRM_ORD_PR
CRM_ORD_OE
Regards,
Suresh