Not sure if it is exactly the same on the N, but with my M645 220 inserts, it works fine. The counter still thinks it is 220, however. The way the camera body knows it is 220 is because a little tab is screwed onto the side of the insert on which the advance handle is located. Two little screws hold the tab in place. If all you ever shoot is 120, the tab can be easily removed so that the handle will wind on through after your 15th shot, "thinking" that you have a 120 insert loaded.
However, instead of doing this, I would sell the 220 inserts to someone who would appreciate them (like me), and use the dough to get more 120 inserts. They are very reasonably priced, even at KEH, which usually runs significantly high.