As far as I remember, wm ex and vanilla wm both use the same items, but in wm ex they were nerfed a lot. While wm ex does have some new traits, it doesn't have items utilising those traits, so items editor should work fine.
Even more strange that the game hangs after manual editing. I tried it once, and it worked perfectly. So I guess that either you made a mistake during editing, or something wrong with your copy of the game.