How can I Customize an CCM error message page

I'd be interested to know if this is possible as well.

I'm guessing that you could sort of hack it by using theming to override the style. For instance, you could set the font of an existing paragraph to some exceedingly small size, and maybe make it white to cause it to effectively disappear. I believe there are CSS commands that would allow you to add text after the now hidden paragraph element as well, but I'm not super savvy in CSS so I'm not sure what the syntax for that would be.