There's the method removeAll. But how caqn I add all the keys again? Like, the keys for moving the camera around?
Dont remove them in the first place. In com.jme.app.BaseSimpleGame.java you can see where they are added and the names of them, just remove those that you dont want.
Also maybe you should have a look at the tutorials, even if they show you things you dont wanna do right now you will surely learn a lot about jme. Theres even one on keyboard input!