You need to put all the images in skins.
You have 6 head images. Create 6 skin and name it head1, head2, head3.
Then in your slot create a skin placeholder called "head".
You key this skin placeholder and at runtime you swap the skins.
If you want to do a combination like head1, body 2, arms 5, legs 3 and shoes 10. You just repeat this process and at runtime you create a new skin and add the skins that you want to it.
If you want to animate images like eyes blink, eyes open, etc. Is the same. You create 2 skin placeholder one "eyes open" and the other "eyes blink" in your slot "eyes". Then you create a skin, call it "eyes1", and put the images (eyes open1, eyes blink1) in their skin placeholders. Repeat the same process creating more skins.
I use this method for my game, the only downside right now is that you can't visualize more than one skin at the same time in Spine editor. So its a shot in the dark animating like this.
The only way I found is keeping a copy of the images under the slots, animate them, and after that replace the keys with the corresponding skin placeholder. Its tedious, but until Spine handle multiple skins at the same time, there is no more choices I think.