The first one you said: I cannot enter it in the editor. It won't let me.
I have some traits that used SHIFT-0, CTRL-0, CTRL-SHIFT-0 , defined in Vassal 3.0 or earlier times, that still work.
However, if I change the SHIFT-0, say, to something else, then it won't let me re-enter it. Same if I just try to define a whole new trait using those command keys.
P.S. I am using Italian QWERTY keyboard (but the 0 is in the same place as on any QWERTY keyboard).