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Yes, they would substitute Charisma for Constitution, as per standard undead rules.
Problem is, they don't.
No Constitution score. Undead use their Charisma score in place of their Constitution score when calculating hit points, Fortitude saves, and any special ability that relies on Constitution (such as when calculating a breath weapon's DC).
Cybernetics aren't hit points, fortitude saves or a special ability. They are gear. Quite often in games cybernetics and magic are antiethical to each other and cause problems if outright aren't even allowed to be combined. It would be quite possible that undead aren't even allowed to have cybernetics due to no constitution score. They could interfere with the magic that sustains the undead.