How can I deactivate the right Shift ¿

The problem you face here is the way the keyboard works is not just a bunch of discreet switches, that would be a lot of wires! Besides a very large chip would be needed to handle all of these inputs.

Instead we use a wire grid supporting a switch array. Think of it this way a group of wires going north to south (A) and another set going east to west (B). Now at each intersection we have a switch tying the two lines together (A + B). This is a switch matrix so it we look at your keyboard we would need 16 - A lines and 6 - B lines (this is not quite correct but lets use this model). The problem we have here is other keys also share these lines so if one switch is making contact when it shouldn't the matrix gets confused. We also have no means to quiet a switch which is were you where heading trying to use software. The only thing you could do is re-assign the switch for a different task. I don't know of any way to alter the base keys only the function keys.

I think the easies way for now is to try an external keyboard to see if that works (USB or Bluetooth). You would still need to use the keyboard to turn the system on but at least for now you can finish writing your paper until you have a window of time to get your system fixed.