This didn't work for me. I think it is an issue with "itemPropertyarentItemEditor" That doesn't exist as an option for me.
Even a reply to all participants would be nice.
I did try that and it would just put my name in. I read on that and it says "username of the user who started the workflow, or caused the event which trigger the workflow."
So if I reply, it will only use my name to reply with. It needs to pull from the previous post username. Using the ParentItem property like you did makes sense if I could find it.