First, let me start off by saying that I have created a 20-lever combo.

Then, let me up the ante by saying I have created a combination lock wherein the combo can be easily and effectively changed.
Switch 1 determines what the switch below it has to be; if Switch 1 is OFF, the one below it must be ON, and vice versa. You can see switch 1 and the switch below it are different values, so the power passes through.
Switch 2 does the same, but since Switch 2 and it's switch are the same value, the power does not pass through.

The top two switches would be in some sort of control room. Preferably, there would be more switches made in this arrangement.