The answer is: Very!
Modifying after heat treating is about five-ten times harder, if not more... It's actually quite an incredible feat that he did so without ruining the knife's surface... Off-center by a little is not a huge deal: Often seen on a Lile or even Neeleys...
It is far away from the edge, so the edge, or even the saw, being softened is unlikely... If it decently done, it is quite a find... I'd go for it just for the uniqueness...
Gaston