How to find the user who made an edit using Lookback API
Per Lookback API documentation, there is a _User field specific to LBAPI:
Note this this field is not directly available in WS API. It is possible to get to the author of a revision in WS API indirectly by traversing from RevisionHistory to Revisions collection to individual revision object and eventually to User on that revision, but it is cumbersome and inefficient.
Here is an example of a LookbackAPI endpoint that returns user stories where ScheduleState was changed from Completed to Accepted:
https://rally1.rallydev.com/analytics/v2.0/service/rally/workspace/<WORKSPACE_OID>/artifact/snapshot/query.js?find={"Project":<PROJECT_OID>,"_TypeHierarchy":"HierarchicalRequirement","ScheduleState": "Accepted", "_PreviousValues.ScheduleState": "Completed"}&fields=["ObjectID","_ValidFrom","_ValidTo","FormattedID","ScheduleState","_PreviousValues.ScheduleState","_User"]&hydrate=["ScheduleState","_PreviousValues.ScheduleState"]&compress=true
Here is an example of result: