You actually can! It just requires cheating.
So quicksave your game so you don't accidentally screw up your files, then go to the .toa-data folder and open the quicksave.json file using Notepad. Ctrl + F 'Warlock' and you should get a result under a line that says 'questFlags'. If you've already completed everything, it probably says "Warlock": 3, go ahead and change that number to 1. Save the file, reload the game, and you should be able to redo the Manor scene.