I understand what you are trying to do. But, this has come up before and it was agreed that it can be done. To change from 12 to a 14" radius is small. Yes it will flatten the board some, but If you have a 1/4 inch board and the fret tang is approx. 1/13" you should have plenty of room. When you sand to 14" radius you will just be sanding the crown in the middle to the down to the edges of the fret board. In other words the edge of the fretboard doesn't change much.