[Kanji_The_Wanderer]

I would recommend doing what you said; exchange in increments. It would be best to change less USD into Yen so you don't have to change it back. Since Yen is actually worth more then dollars you will be losing money, and I am sure that you do not want that. So instead of changing more then you need, make it less. Then if you require more after, just go and change it.

I am not sure how to exchange currency though, since I have never traveled anywhere that doesn't use American money. Maybe you can do this at a bank or in an airport?