How can we modify the stock status bar artwork (signal bars, wifi bars, battery status, alarm clock, etc...)?

I know the artwork is in the Shared UIImages folder now. I tried changing the alarm clock icons to start by putting Black_Alarm@2x.png and Silver_Alarm@2x.png in the UIImages folder in my theme and nothing changed. They are the correct high res size at 20x40 pixels.

Anyone done this yet?