As I found out earlier, the rate of MOSFET modification was very sensitive to torture voltage. Like, at 38 V it was barely progressing, but at 42 V it was pretty fast.
I thought that if I control current, the rate of change would be more predictable. And indeed, if I take the initial rates of change, they seem pretty proportional to current:
Except that for the first point, at torture current of 0.01 uA, I essentially didn't detect any effect at all. It might be because the current was not actually delivered to the mosfet gate (it may have leaked through the switch for example (see circuit), although I checked switch leakage beforehand). Or it was because the mosfet wasn't completely fresh... Anyway, there's not enough points to draw major conclusions yet...
And as you already know, this initial rate thing doesn't tell the whole story, as the threshold voltage ceases decreasing and starts to increase at later time.
Curious to see, what will happen for negative torture. Also curious to see if transfer characteristic is any different to what I got before.