Halfskin by Tony Bertauski

Halfskin by Tony Bertauski is a interesting book set in the future where most humans are injected with biomites, tiny machines the size of a cell in the body. These robots can increase athletic prowess, make eyes different colors, heal injuries, you name it. However these biomites will constantly repurduce, transforming the human cells into stronger biomites. This would be amazing, but under a politician named Marcos' laws, people with more than 50% biomites are no longer human

-and M0ther, the all-seeing computer will shut down your biomites. And you know what happens then. However Cali, a bioengineer, with 49.9% biomites, and her brother, Nix, who has 50% do the impossible-they make biomites that M0ther cannot see. After absorbing these biomites, they shut down the ones that M0ther CAN see, and suddenly can interface with machines, all with all-human Marcos' minions hunting them down for being more machine than human.