Don't you do that with a CoC as well? Short of writing a long list of things that may and may not be said, you can only give a vague "please be kind to each other", but the concrete judgement what is and isn't kind depends on whether your views align with those in power.
My experience is that vague rules are both a recipe for corruption (where the enforcer's friends are exempt from the rules and the argument is "that wasn't rude, the person deserved to be called a shithead") and the troll's playground, because toxic people that want to cause trouble are great at figuring out the pain points that get to their targets but don't cross any lines.
I believe that enforcement is important, not rules. You can always have a more specific policy for the moderators to guide them and to develop the team's response, but that shouldn't be part of the rules.
It's true that it's not 100% fair that you might get kicked out for breaking a rule you didn't know existed, but to me that's collateral damage I'm more than happy to accept (and I've been on the receiving end of a "you crossed a line" talk).