You can directly modify the values of individual skin point weights using the Component Editor. The Component Editor lets you easily set specific skin point weights to particular values.
If you want to shape the deformation directly and are not concerned with specific values, you can instead paint weights with the Paint Skin Weights Tool. See Painting smooth skin point weights.
While you are editing skin point weights, you can reset the weights to their initial values at any time (see Reset skin point weights to default weights). You can also prevent indirect changes to skin point weights (see Holding smooth skin weights), which can happen if Maya is normalizing the weights (see Smooth skin weight normalization).