How to modify this toy piano circuit?

Hi!

I am new to this forum. I have recently seen a circuit diagram of Toy Piano which provides tone in 5 different pitch levels. I planned to do that project, but with few modifications. Can anybody tell is it not possible to get different types of tones in different ways? If possible, can you tell me what are the modifications to be done to this particular circuit?

Thanks in advance,
Sudheer.