Thanks for all the comments.
I have tried to change the notes at Narita Airport and was refused that they do not change Yen for Yen, even though I have changed some SGD to YEN as well.
Well, in Tokyo, I went to a Japanese restaurant for dinner and they gladly accepted the old note for payment. Thereafter, I tried again at a 7-11 store in Ueno and they accepted as well. Was real glad that I managed to do it without much fuss.