1. A computer-implemented method for customizing the appearance of a digital object, the method comprising: receiving a modification to a then current model definition for the digital object; upon determining the then current model definition satisfies at least one exclude override rule, modifying a copy of the then current model definition, as specified by the exclude override rule, without modifying the then current model definition; and generating, by operation of a processor, a display of the digital object from the modified copy of the then current model definition.