How do I stop AutoPPC touching a specific campaign?

Settings › Protection → Hands-off campaigns. AutoPPC will never propose any change there — no bids, no negatives, no budgets.

Alerts still fire, so you will still hear if it starts spending abnormally or a product becomes unbuyable. You just will not be offered a fix.

For narrower protection: brand terms are never negated or bid down, and protected families are never negated. Both are lists you control.