In addition to what James said, I'm reminded of the mechanism to change screen resolution in Windows XP: It automatically resets to its original resolution in X seconds, in case you can't see the screen. This is so people can't break their computers in one moment of weakness.

A similar thing could be done with self-modification. Self-destruction would still be possible, of course, just as it is now (I could go jump off of a bridge). But just as suicide is something that is built up to in humans, failsafes could be put in place so self-modification was equally deliberate.