Permanent Means Permanent

The five minutes passed. Then, nothing. Jon and Karyn looked back and forth from the clock to each other. Five more minutes. "I guess the wishes really are irreversible." muttered John. It made sense. His grandfather was no fool. Surely he had tried it, and he had failed just the same. If it had worked, he would have mentioned it in his message to John. "Maybe we can still wish it away." suggested Karyn "Your hair did look like mine for those five minutes."
"I guess there's only one way to find out." Taking the stone, he wished "I wish that my hair was back to the way it was before."