Maybe add a worm in the apple as well? That would be unique.
Does that go on the outside of the MacBook? Or inside, under the cover.
You have to crack the back casing open and put a colored piece of plastic in there. Definitely voids the warranty.
I have seen people color them with markers or paint before though. This probably still voids the warranty, but is less risky.
Just ordered one, you're getting positive rep if it's as good as you say...
Just ordered one, you're getting positive rep if it's as good as you say...