The idea of skinability is ability to the skin completely change it completely with your own css.
The amount of work to override the skin and amount of work to disable it and override then are equal.
So, do not concentrate on "disabling". Just do what you want.
All you need to do is to define classes mentioned here
section 7.9.7. Definition custom Style Classes
We also include "plain" skin into upcoming release. "Plain" skin will contain zero look attributes.