The Death Star II reactor core has a shield protecting it. However an extremely skilled X-Wing pilot may be able to disable this shielding by destroying the power regulator in the tower next to the core...
The HoTAC rules state: "While an AI ship has a stress token, it may still perform red maneuvers and acquire tokens, but cannot perform free actions."
So even if the AI is stressed and rolls a red manoeuvre, it would still perform that manoeuvre.