material master

dear all,

I have a scenario, where i have material X which i am selling to customer . after few months I have done

some modifications to material X .

Now we have Material X - which is prior modification and still we sell to customer

Material X - after modification ,we also sell this material to customer without changing material number.(we donot want to infact )

How do we differentiate single material X with two different attributes .?

thanks

umesh