2 button jacket turned into a 3 button?

Probably not. As far as I'm aware, when a 2 button jacket is cut, it is usually cut with the assumption that the 2nd (or bottom) button will not be fastened, and so fastening it usually causes excess fabric to accumulate between the two button holes... so adding a third button and then fastening the second would probably result in the jacket looking quite awkward. If there's sufficient space above the top button you MIGHT be able to do it, but again, if the jacket is cut well, I wouldn't hold out much hope.

It is a question of the lapel roll. The lapel roll will end on the top button, i.e. a two-button coat has a longer lapel roll than a tree-button coat. Only exception would be an Ivy League style sack, although having three buttons the lapel roll goes down to the middle button. Even that would be somewhat difficult to add, as there would be two machine- and one handmade buttonhole. Don't worry, two button coats are on their way back.

Bengal, I agree. I actually prefer a 2-button jacket when I'm not wearing a tie. I think the look is much more stylish than a 3-button with an open shirt collar underneath. There was a GQ some months back with Clooney on the cover. He was wearing a 2 button suit with no tie. A 3-button suit would have looked a little strange. Y77