Baby steps. Full robot mode seems like more than the current system can support… but a cyborg that needs power to live (say, to run an artificial heart or something) might be more doable.
Firstly, you need a bionic with the ‘this constantly uses power to keep you alive’ property, like the aforementioned artificial heart. It might have some good effects, but they’re overshadowed by the ‘if this stops working, you will die very soon’ thing. Once you have a bionic heart implemented, then you can give it to a disadvantageous version of the bionic patient profession, and have the basic effect of a character that needs power to live. Next, you’ll need bionic limbs that need repairs instead of natural healing and bandages, and bionics that consume power to reduce the need for food/drink.
Once those things exist, you’ll have everything you need to make a proper robot; model it as a human, all of whose body parts are mechanical and need repairs instead of healing, and who needs power instead of food/water to live. Probably also tack on some appropriate immunities, like mutations, infections, and disease, and you’re good.
