The “DO NOT USE THE + (positive) Terminal. S & – (signal and Negative) Only” sentence is about the pins of your control board.
There are 3 pins for each endstop terminal on the board. We don’t use the “+” pin. Only the “S” and the “-” pins. Pay attention to the diagram because all terminals are not oriented in the same direction. The “-” is always the middle one, but the “S” is sometimes on the right, sometimes on the left.
The switch itself has no polarity because there are no active components inside. Imagine you have only one long wire that goes from the “S” pin to the “-” pin of your board (no polarity right ?). When you press the switch, it is equivalent to cutting the imaginary wire.
You can totally use two black wires, connect one to “-” and the other to “S” of your board, then connect them to “COM” and “NC” of your switch in random order.
Your proposal will work, and the opposite will work too.