While I don't have a character with that background, there is a skill for building and repairing cyberware in the core rules. Of the top of my hat I can't remember more than one character who had that skill, but tinkering with your cyberware isn't impossible. That's what your friendly neighborhood street docs are for. For example, this guy's 'ware does not look like it still has all it's warranty seals intact:
http://markzug.com/prints/single-gallery/2851037 :-)
Unscrewing the cyber-pinky of my Cyberarm (complete with built-in Renraku Deck) and adding a cable tap to the end of it isn't quite so different from attaching it to the deck itself, don't you think?