From positive voltage torture kinetic, I though that positive voltage might be doing two things at the same time: change gate threshold voltage, and undo the changes. Because the timelapse looks like this: first, threshold voltage goes down, then it turns around and goes up and essentially returns to where it had started.

So I decided to use it to restore the lowered threshold by applying large positive voltage, that is large, but just a little smaller than what is needed to make the gate leak, and the threshold start to o down.

It works!

On this timelapse:

First, I reduced the threshold voltage of a mosfet by applying large negative voltage (23-36V, I actually was pulling a current). Then, I applied positive voltage. This caused threshold to rise.

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I also seems to have successfully restored a mosfet tortured to the end with positive current, here. That mosfet was behaving bad. When I inserted it into gate threshold measuring circuit, it drifted like crazy. After feeding +35V to gate for a few hours, its threshold didn't change much. But it doesn't do that awful drifting anymore!