You revelled in the feeling of your new monkey tail and the things you could do with it. But then you thought "why should I be the only one to enjoy this?" Going back to the Chronivac you found the option that let you change humanity as a whole. With a few clicks you had things set up so that every human on the planet would grow a monkey tail as soon as you hit enter. You also made it so that no one other than yourself would be aware of the change. You didn't want there to be mass panic after all.
With everything set up you hit enter and went to a window to watch the changes unfold. At first nothing seemed to be happening. But as you watched people's clothing shifted and changed. A hole appeared right where everyone's new tails would be growing from. A small lumped of skin began poking from the end of people's spines. It grew and grew until everyone had hairless tails swinging behind them. But they didn't stay hairless for long. Soon fur whose colour matched with the rest of the hair on people's bodies grew out from the tails. Just as quickly as it had started it was over and everyone continued with their day not even aware of the massive change that had just occurred.
You were delighted to have witnessed such a beautiful spectical. Even more so knowing that you had been behind it. But what to do now? You could do anything you wanted, so you decided to...