In Admin -> Global -> Cross References, you can set specific cross references, such as SAP, as Externally Managed, but I think you can also do that in the data object when you are setting it specifically in code, if needed.
1. GSM.ExtManagedCrossRef.Enabled needs to be set to true to turn this feature on.
2. Users with the role [EXTERNALLY_MANAGED_CROSS_REF_ADMIN] will be able to edit those rows marked as externally managed.