With T2Fix, all you have to do is run setup again and ensure the mission and resource fix is unchecked on the component selection page. The fixed missions will be fully uninstalled and the original, unmodified missions will be reinstated. No manual configuration is required to do this.
I believe the pathfinding issues on the stairs in Angelwatch were fixed in more recent versions of Thief2 Fixed. T2Fix offers the same mission patch as Tafferpatcher did, but a much more recent version of it.klatremus: Sorry. Looks like I misunderstood you previously. I believe there is even more changes that doesn't always make game easier. On Tafferpatcher 1.25 people walking on stairs in Angelwatch have tendency to get stuck at the middle of stairs leading upstairs from your position. If you manage to get upstairs above them, then after returning to stairs they block at the middle of even higher stairs. So getting to Ballroom is tricky. No idea if the same thing happens in T2Fix though.