I know how to copy face from NPC to PC, or from PC to NPC, but I don't know how to make a PC's face as the default face of a race.
Is it possible to do that?

If I remember rightly I was able to use Bash to select the save game of that char and copy the face to an esp I had made called FaceResource.esp.

the names not important just had meaning so I didn't load it with regular mods, then load that esp with the mod your making and create the NPC, open
the NPC with the face you want (was called sg I think) copy the face and paste it to your new NPC, should be all good, it's been a long time
tho so I'm hoping I remembered right