Newbie question: How could I change just the head to a look? I mean, I'd like to keep the whole body and replace only the face.
Not trivial.
The way I do it is using the character fusioner plugin, but I don't do it often, so it's hard to make a step by step guide.
From what I can recall, you save the look you want the head as an appearance preset, then load the look you want the body in a scene, load the character fusioner plugin, add a minimal amount value of the appearance with the head you want, then the morph you want will show up in the female morph tab. Set the unwanted head morph to zero and the wanted head morph to 1.
In other words, the look will have:
Unwanted Head morph > 1
Wanted Body morph > 1
When you add .01 value from the other look, it will be like this
Unwanted Head morph > 1
Wanted Body morph > 1
Wanted Head morph > .01
Unwanted Body morph > .01
Then you remove the unwanted stuff
Unwanted Head morph > 0
Wanted Body morph > 1
Wanted Head morph > 1
Unwanted Body morph > 0
It doesn't always work. Sometimes the neck will just collapse into the sternum, Idk why. So you can try other plugins, like the mass morph merger.