I am not sure I understand the scenario, but the general approach is to have a rule on the object that:
1) Has a condition with WAS CHANGED (or WAS ADDED or WAS REMOVED) to check that a reference attribute was changed.
2) Has FIND action, if necessary, to get other objects. Here you can use prefixes "Changed", "Added" or "Removed" to refer to an object identified in the above condition.
3) Has an assignment or INSERT action to assign the found object (or the changed/added/removed object or its referred object) to the other reference attribute as necessary.
This is a common design pattern used in many applications. The Aware IM User Guide has detailed information on each of the steps described above.
