If you want to cancel a lane change before it starts, you can either use the turn signal or press the notification pop-up on the touchscreen. And no, this isn't an opportunity to go AWOL while you're on the highway -- the car won't change lanes unless your hands are on the wheel.
The update also lets you enable Navigate on Autopilot at the start of every trip. If you do, it'll kick in every time you enter a navigation route and reach the highway.
You'll still need to have purchased an Enhanced Autopilot or Full Self-Driving Capability pack to use the feature. It's only available in the US for now, but it should come to other countries once Tesla has received the all-clear.
It's a significant change for Tesla. The turn stalk requirement came into place to make clear that drivers were still liable for what happened on the road. Clearly, it believes that the combination of the option and notifications fits that bill while reducing the demand from the driver -- you know exactly what you're getting into, even if you're not using a physical toggle every time. While fully autonomous driving is still some distance away, the update gets you closer to that goal.