You can't change the names of the controls if you want them to continue working properly with the Platform behavior. You can, however, change the key that uses the control. So you can use Z if you want, you just can't name it "P1 Jump."
I was unaware of this until recently, so I now have to go back and edit all of my Platform School tutorials, since I said it was okay to change the name. I just never changed the name for Jump.
Odd, though, that you can still move left/right if you rename "Move Left" and "Move Right."
Also, you won't be able to make a separate set of controls for a second player right now. Construct doesn't yet support multiple players, or multiple player controls. You could do it manually with key-presses, rather than control-presses, but you will lose some functionality (most notably, Jump Sustain).
You can work around it by making an event to tell your platformer to jump when YOUR jump button is pushed, and then set the default jump button to something out of the way.
Actually, no... for the reason mentioned above. You'd lose the Jump Sustain ability. This might not affect some games, but Mario definitely has Jump Sustain.