I wasn't quite sure what to expect as I started removing the head from a Monster High Ghoulia doll. I did it with that small screwdriver you can see in the photo. The construction turned out to be similar to Barbie's. The only reason for that odd round knob seems to be that Monster High dolls have such a thin neck that the post could not be attached to it without making that part thicker.
Next, it was time for the hair to go. I cut the hair as short as possible and then used the wide tweezers to scrape the inside of the scalp to pull the hair in. When everything was inside the head, I used the other tweezers to pull it all out (those tweezers are easier to use as you press to open them, so their "default position" is closed).
After removing all original paint using acetone, it was time to apply some new. I used Folk Art's acrylic paints and mixed the different shades myself.
I had thought that I would do a reroot, but I came across the perfect yarn for her hair and it was too thick for rerooting (or at least I couldn't figure out how it could be done). So, I used a sewing machine to sew the strands together for easy gluing. It's fairly easy when you arrange the strands on top of baking paper and sew at least twice across them. When finished, you just need to rip off the paper (by this time, it will have so many holes in it that it will be easy to remove).
I used three strips: back, front, top. The top one is sewn from the middle to make a parting. I used PVA glue to glue the hair in place as it has worked with a smaller doll I customized earlier. If it won't hold, I'll use super glue to glue it back. Even if I have to resort to that, the first gluing won't be a waste of time as I expect super glue to work better when there will be a smooth surface (the PVA glue strip in the hair) against a smooth surface (the vinyl).
And here Ghoulia impersonates Cousin Itt as she waits for the glue to dry.
Finally, photos of the finished doll. She's wearing a business suit for now as I haven't yet made her outfit. The boots are the ones I made for Draculaura a while ago.