In the Save Game Modifier you can unselect the Observer Status and then hit apply & it sends a "fixed" saved game called scen.ees. However, for the Observer status the change isn't really applied.
The Observer Status comes automatically after a multiplayer game is played a while (maybe 1 hr) under LAN. Normal Human players turn into "Observers" after some time and then you can't control them any more. This is under Windows-7 & Windows-10.
If I knew the HEX addresses of where the Observer Status was set, or if it came after an easily identifiable hex pattern, I could fix it myself using a HEX editor on the save games.
