if he is changing sights, all he has to do is take off the slide and take it to whoever going to do the work.
no ATT needed.
I'm not familiar with the M&P but go to forums specific to that gun and see what others have done.
A gunsmith will likely just hit it harder than you feel comfortable doing yourself.
Unless there is a specific trick or screw that you don't know about, which is why I suggest going to an M&P forum to learn about your firearm.
If all else fails, Casey is great to deal with.
Edit.
Ok, I was bored and just did a google search.
the sight dovetails are tapered. you have to push the rear sight towards the ejection port side of the slide.
There is a spring and small nylon washer under the slide that work with the safety plunger, so be careful not to have those fly in your face or lose them.
I suggest putting a plastic bag over the end of the slide so if/when the spring comes out its contained.
Really, secure the slide in a vise, get a brass punch that is large enough to take up enough surface area on the rear sight to spread the force and not mark it, and have at it.
Its what a gunsmith will do.
