How can I quickly switch between materials for a group of Faces? Individually re-assigning each Face to another absorption spectrum is of course one way to go. But switching each Face to a second alternate material is very slow. Is there a better way?

EASE 4.0: Yes, there is. The easiest way is to define an Object containing all these Faces. After that you can go to theObject's properties sheet and set the Wall Material of all Faces with a single click.
Of course you can also use the method described below.

EASE 3.0: Yes, it is. Although 3.0 does not provide grouping functions there is a good quick way to assign Wall Materials to a dozen Faces. Please find the menu command "color and material coupled" in the Face Tables Window. If you just assign the same color to each group of Faces EASE will change the Wall Material of all Faces with the same color in one step when you change a single material assignment. But this only applies to the table.