The black areas are conductive and is what gives the sensor variable resistance so insulating paint won't work.

A paint kit that repairs heated rear windows is a possibility however we don't know the resistance per area of the old and new paint.

Have a look at the center terminal, go to the right and down a slight bit. You will see a thin white line. Look further to the right and you will see more lines. These are laser cut lines to adjust the sensor linearity and calibration.