Classification System For Materials (class 001)

A customer of mine needs a Classification system for materials (class 001). In this class he will include some characteristics which are plant depending, for example the MRP controller.

The character cross-reference to the field on MARC is given, but in the materials master there is no result shown. Why is it blank, because the classification is on MARA level. No, the customer asserted, that it is possible to customize this to plant level. And then it is possible if you want to change the material to select the classification over the plant.

Is this really true? And if yes, what are the consequences in other applications?