Seems like a "Spider-Man 2" situation. The oscillation between both states was due to an ongoing identity crisis, brought on in part by his transformation. He's resolved that now, so he doesn't associate his body's new powers with Germa anymore. Thus, he retains them, but understands that they're neither a curse nor something that makes him Germa. That's why his eyebrows return to normal. He's reconciled this crisis. It's part of his self love, to accept and embrace every part of himself. At least that's how I understood it.