Material classification with plant as additional key

Hello!

We want to clasify our materials with additional keys. Some keys are classic organisational entities like plant,

sales organisation and destribution channel another extra key would be country. We were abel to create the extra

classes with the extra keys, but couldn't find a way to integrate those in MM02. I managed to integrate the class

with the country as extra key in MM02, but I can not change the country field in MM02, so I'm maintaining data

with the field country empty.

Is there any way to integrate a class that has the key material number and plant in transaction MM02 with full functionality?

Thanks & best regards,

Horst