does the system allow to change Unit Cost for the remaining amount, after the PO line has been recei

Processing option set is for detail line protection to 999 and to enable the cost fields. We get this error when a po line is revised to change the unit cost it shows the Last sts to 400 and next sts to 300, there is no Order activity rule set for lst sts 400 to have allowable next status to 300, so the error is fine - sts not defined in Order activity rules.

how can we change the unit cost in F4311 (P4310) where the line was partially received, in my opinion you cannot change unit cost when you have the same line waiting on payment in F0411(supplier ledger inquiry) you thoughts please help