In a way, Yum is right, you don't really change the shape of a muscle. On the other hand their are some tricks you can use to change the shape of an isolated part of your physique. First, making the bigger will accentuate the shape you already have, making a little peak appear to be a bigger peak. On the other hand, working with a muscle system, such as the bicep, one may be able to force hypertrophy in a given spot which may result in directed pressure within the muscle. This will often result in a change in the appearance of the muscle.
My suggestion for developing the bicep peak is to do reverse grip curls with a straight bar. Forgive my lack of specificity (can't find my kinesiology book) but this exercise tends to hit an inner and under part of the bicep resulting in a fuller peak.