Clean work, but how is this related to the Kramer mod (which is a mod that specifies holes to be made in the driver grill, for the sake of decreasing reflection in the driver assembly)? It seems to be purely cosmetic?
You're adding material (metal washer, rubber washer) in front of the driver instead of removing material, it's actually opposite of a Kramer mod I would say.
That's the "quarter mod", named that way because you would put a quarter coin on the center of the foam earpad and cut out the hole around it.
And even that mod does not involve adding washers around the hole, I can't imagine them doing any good to the sound quality, in fact they are probably bad because they would cause reflection of sound projected from the drivers.