You can slap bacon on your hamburger as much as you like. Shufflesome stickers are not like hamburgers. You can't slap on just any art. Unlike bacon, some art can't be chewed and swallowed. For example, Spider-Man won't appear on Shufflesome stickers, unless there are agreements that entitle you to use Spider-Man art. For your custom sticker design, i understand it is tempting to submit designs with graphics from Hello Kitty, Winnie The Pooh, Spider-Man or any other such beauties. But there are limits, which i have described. Submissions for custom designs are strictly denied, if you resuse graphics without permission from the creator or licensor.
A brand that is popular must not be easily obtainable. Don't take art for granted. By all means, let Spider-Man's people know you want his powers on your Shuffle. Body and soul need challenges.