It also has a 95% chance- or greater- of changing his personality and making him a bad person. His previous ethical or moral reluctance to steal and aggress will be short-circuited.
And he's asking you to be the one to push the button to start the device.
Would you do it?
What if it takes two people to push buttons simultaneously? Would you be willing to share half of the responsibility? Remember, your friend wants this. What if there are millions of buttons that would all have to be pushed to activate the experiment? What if "authority" figures tell you it is your duty to push the button, and your other friends, family, and neighbors all agree? They say you should be ashamed if you refuse. Why do I see shades of Milgram?
This is the same thing as voting for a decent person who wants a political office. Only, in this real-world experiment, those who push the button and those who refuse will all be victimized by your friend after he gets what he wants and is changed.
How can you consent to be among those who do this to a good person?
*Of course, it's not really an "experiment" since it has been done multiple millions of times with the same results- you know how this will end unless you are successful at deluding yourself.