The archive itself knows if it is loading or saving. So Ar.IsLoading() or Ar.IsSaving() will save you the need to pass around the boolean.
That said, I think that you are going to be forced to have a switch that does different things for this kind of saving. Inherently what you are doing on the save step is storing the specific pieces of data necessary to reconstruct the state and then on load you’re actually reconstructing it, we actually do much the same for Actor components when rerunning construction scripts: cache off some state, then reapply after the construction script runs)