Natural Scroll Direction: On with trackpad, Off with mouse I already tried this:
Changing trackpad scroll direction with AppleScript in Yosemite

But it didn't work.

What I need is when I use the internal macBook Pro trackpad, natural scroll direction is enabled, and when I use an external mouse, it is disabled.

If this is impossible, how about the following alternative: when I plug in a mouse switch to "non-natural" scroll direction, and when I disconnect the mouse switch back to natural.
Hi just found a great app that totally fixed this and so simple! You can set the scroll direction for each device separately.

SCROLL REVERSER
http://pilotmoon.com/scrollreverser/