Don't lift off all the way in high speed direction changes. When you lift off all the way the diff opens up and the car wants to rotate a lot more. staying very lightly on the gas will keep the diff semi locked and the car wont want to turn as much.
Negative wing is exactly what it says on the tin. Front leading edge is higher than the rear trailing edge. It will still produce downforce as long as the underside rear of the wing is producing some sort of up wash. Generally it isn't very efficient and you don't loose that much drag for the downforce loss but in spec series like F4 where you have too much rear aero anyway you tend to see it being ran to both help high speed understeer and top end speed. The only other example I can think of is in the modern spec era of IndyCar, teams tend to run negative wing angle at the Indy 500 just to cut as much drag as possible for quali.