You can stop Shart changing her hairstyle in the base game. I've done it once.
After defeating Kethric and everyone gathering in Moonrise throne room, refuse to allow Aylin and Isobel to join camp. Demand answers for Shart then and there, and when they balk, refuse entry.
Shart didn't learn about stuff and went into Act 3 w black hair.
This is like asking how you can turn off the light of your new wristwatch and receiving the suggestion to amputate the entire arm from the shoulder.
