They are pressed in. You can fix it yourself (assuming you can get the part & have the mechanical ability & tools) but it will not be an almost invisible fit like the original. The reason is that the gun was polished with the pin in place prior to bluing. If you are mechanically inclined, it is just a matter of patience and trial & error. If you send it back to the Factory for repair, they can fix it either one of two ways............
By putting a new one in and fitting it just like it was originally, but that will require them to refinish the entire gun. If it is in excellent original condition, I would not want it to be refinished. The second choice is to put an older style stud in which has more of a rounded and visible fit, but it will look like an old style pin that belongs there. If you can find an older M&P revolver you can look at it and see what I mean.
Of course you can install the original type yourself and just get it to fit as well as possible without polishing it installed in the gun. Like I said, it will work, but it will be seen.
Chief38