![P90ReverseWoundReversePolarity](https://www.mcha.nl/wp-content/uploads/2015/09/P90ReverseWoundReversePolarity-364x273.jpg)
“open the pickup, take out the bobbin and flip it over so that the top becomes the bottom and bottom becomes the top, rotate the magnet 180 degrees so N becomes S and S becomes N; now it is reverse wound reverse polarity without having to change any wires”
Source: http://forum.gibson.com