How do I keep an item from rolling cost once I input a manual cost

Summary

Item use to have a work definition, now its a purchased item, but each subsequent cost roll overrides manual cost with incorrect rolled cost

Content

Have item A, use to be manufactured at Org so a Work Definition (WD) exists, now its a purchased item & I input a cost into a scenario.

Since you can not end date a WD, each time we rollup a subsequent scenario - purchased cost gets changed to a faulty rolled up cost.

Suggestion 1)  Change "Include in Rollup" flag on PIM to NO, to stop rollup.  I tested this and it won't roll, but it also won't include this item at all in any parent assemblies that use it.  (Suggestion failed)