Photoshop actions. Photoshop actions for cropping exactly the same way every time. That's how. Retexturing the hairs themselves actually takes more ingenuity and is thus more fun.

I'm so glad you enjoyed Girl Genius! You're welcome for the link-- it's the third webcomic link I've used at Garden of Shadows. I know fans, if not the Foglios themselves, have been considering Team Tarvek and Team Gil T-shirts as kind of an ironic... thing... and I can't help but notice that Agatha's hair color is pretty much Comburent...