lol.
You can't condition your face and head, but you can condition your own perceptions and you can practice rolling the head and clamping the jaw and so on.
Mostly, you are better off learning how to slip, duck and eat head shots on the arms and shoulders same as every other boxer out there.
the point your raise is good though, I find that when I watch demonstrations of traditional martial arts, there is a propensity for leaving the head wide open as a target. Often there is failure to shrimp, tuck and protect the head. It is the most vulnerable area and it is the one area that any fighter worth even the tiniest grain of salt is gonna go after. body shots are nice, but on a conditioned fighter, that's a real slow road to the finish.
so, learn up your slips, your bobs, your clinch work, your footwork, your ducking skeelz and your ability to seam feed, pat, chop and destroy incoming shots to the head.