Dear John
the inheritance depends on "template". If I rmember correct: only if you have set upproperly the "relationship" with "suitable" inheritance termplate you can "overwrite" on target without the risk that if source changes target will be adapted. But Identifier are some kind of "special" in context of inheritance. Check:
Editing Inheritance Templates - Specification Management (EHS-BD-SPE) - SAP Library
Context: Permitted change options
C.B.