Why not?

You sat with you shirt and sweatshirt pulled up as Mr. Knight applied ink to the center of your back. You could feel the strokes of his finger as he applied the tattoo and see it through the array of mirrors that you both had set up. After a bit he pressed his hand against the ink and you could feel a brief flash of heat. When he pulled his hand away you could see the tattoo had been applied. You then stood, allowing your shirt and sweatshirt to fall back down. You then went to work applying the same tattoo to his back. It took you longer, your hands and mind less practiced. Eventually, you managed to get it right and placed your hand flat against it. You felt the flare of power and when you pulled your hand away it was a real tattoo.

"Holy shit, I did it!" you said.

"You did. Excellent work," Mr. Knight said. "Now we need only wait until the hour has passed and you can use the coin again."

"What happens if you flip and get the same result that I do?" you asked.

He frowned for a moment and then shrugged. "In that result, we would find ourselves no different than if the tattoos weren't applied. You would look as you do now and I would find myself in my female form. Or we would both be as we are normally, in our male forms."

You nodded, looking over the notes. That made sense based on what you were seeing.

"As a matter of fact," Mr. Knight said. "Perhaps we should both flip for this first time. The data would be interesting to have."

"Makes sense to me."

With that, the two of you waited, you looking at the objects around the room and him working at his desk. When the hour was up, you lifted up your coin and he did the same. He seemed somewhat engrossed in his work, still moving things around his desk and looking down. "Ready?" he asked.

"As I'll ever be." You both flipped your coins, waiting to see the results.