Changing your layer.

Just wondering if it is possible to change your layer in a script. Looked at the manual for the layer mask and it is not really touching on what I am looking for, the instance I am speaking of is when you are in a cave or under a tree the sun will not touch you but when you step from under your shade the sun should beam and cast light on you so I was wondering if it could be done? Now I may be going about this the wrong way but any help is appreciated.

 

http://unity3d.com/support/documentation/Manual/Shadows.html