I agree with Midnite. I think it's hardly likely that [spoiler] Petofi took over Quentin's body in the unchanged timeline and that it was HIS spirit in Quentin's form haunting Collinwood because in unchanged history, Petofi never met Barnabas who was still chained up in his coffin and Julia hadn't been born yet so the idea of time-travelling never even occured to him, much less the means to get there.
However, in one of the older threads, somebody pitched the idea that in the Gerard/Daphne haunting, Judah Zachery had really been the one haunting Collinwood through Gerard's form. Now that idea I can buy since Judah did possess Gerard in 1840, something that I believed happened before in the unchanged 1840 before Barnabas and Julia went back and changed things. I do think that the circumstances of Judah's demise may have been changed due to Barnabas and Julia's presence. Maybe Judah really had been strangled by Gabriel, or Daphne or Quentin put a bullet into him, or maybe Gerard as Judah had been exposed and destroyed another way. Who knows? [/spoiler]