In question 630 about the future, one answer was that "If it's true now that you will lose a finger next year, then you will lose a finger next year and zipping into the future isn't going to change that."
What if the person cut his/her whole hand off? This would obviously show the loss of the finger, but with a new addition (or subtraction, ha ha!) to the picture: a missing hand.
Wouldn't this prove that one could alter the future if it was seen?