Part material selection within an assembly

Hi, I would like to create an assembly containing a number of parts and make it so that at each regeneration I can enter a value to a parameter that changes the material of all parts for me.
Example:
I create parameter MAT that can have value 0 or 1 depending on whether I want aluminum or copper.
Assembly A containing parts B-C-D having Aluminum as material so parameter MAT equals 0.
I regenerate and set the parameter value to 1 getting parts B-C-D with material Copper .
How can I do something like this?
Are there other ways to do this kind of operation?
I use Creo 11 with the AAX extension.