I know this topic is older, but I figured I would put in my two cents! Okay, for the hair, rerooting can actually be done much easier on an MH doll with the rerooting tool method and Fabri-tac glue inside the head. Dollyhair.com has a tutorial on how to do that as well, and I personally recommend the reroot tool sold by
debi255 on Ebay. The Dollyhair.com ones are a bit unwieldy and break more compared to the ones on Ebay. Get the standard size one, the ones for rerooting reborn eyelashes/etc are good for smaller dolls like Volks/Obitsu 1/6 heads that don't have pre-rooted holes, but Monster High heads are
huge and can handle thicker plugs, which gives a nice full look.
Also, since the Monster High heads are so big they're perfect for squirting some Fabri-tac glue inside! The stuff dries and makes a reroot as secure as the slower "lock" method and the needle and thread method, but to each their own, rerooting is entirely about personal preference!
Now, the bald parts, I assume you're thinking of a design a bit like Venus McFlytrap's? There is a trick that some MH modders use that was discovered quite by accident while boil-perming. They noticed that a strong boil-perm would usually close up the holes for earrings which are much larger than reroot holes. As long as you've been careful with derooting her so she doesn't have GAPING hair holes, some customizers take a hot glue gun, WITHOUT the hot glue in it, and run it over the holes. It seems to seal the surface of the vinyl back together, it doesn't go all the way through but it gives the skin a smooth, hairless look. Now, if you're doing a buzz-cut on any point of her hair, I reccomend that you paint at least that area of her scalp the hair colour you've chosen, and to reroot super thickly (think how the scalp line is rooted, and do that the entire length of the buzz-cut), and when you're done and have secured it by whatever means you want, cut the hair until it's nothing but short bristles so it looks as if the character has gotten...you guessed it, buzz-cut!
I hope this helps a little. I'm sorry I don't have any tutorials handy, this is more of a "tips I've heard from other customizers" type deal.