The most important thing about changing kenpo (I got this from Dave Hebler, with whom I was privileged to study for a while in 03 and 04) is to remember that the techniques aren't really self-defense techniques.
They're lesson plans. Nothing more.
If you understand what they are intended to teach, then adapting them to fit a specific student's needs, or to accommodate for changes in reality -- such as the fact that nobody attacks with that overhand Psycho knife stab anymore -- is pretty simple.
Just my 2 cents.
Yet interestingly enough, people will say that the 'stats' show that that is exactly how people will attack...the overhead and the straight thrust. Personally I think it'd be wise to train for that, and a slash, a rapid fire pumping action of the knife such as we'd see in a prison knife attack, as well as stationary knife attacks, ie: having the blade held to your throat.