I don't know if rehearsals would do any good

Really, this is how I feel. I'd be really surprised if a setup like that actually worked. I'm not sure Harry is supposed to actually believe (with any confidence) that it works for Chaos. Ultimately you know and everyone else knows that it's just a charade, and that really your "nonconforming" is just conforming one level below surface: You stand there and take abuse that you know to be insincere, and then get a pat on the back about it later, just like everyone else did on their turn.

Hopefully CMR has a better exercise in mind. A really good anti-Asch training tool seems like a great thing to have.

You could mock obviously true statements to practice withstanding opposition.

The danger with this seems to be that you'll also be developing skills for attacking correct positions. It's training you to develop tactics for entrenching yourself in incorrect beliefs. Also it seems to lend itself to the view of arguments as status conflicts rather than group truth-investigation (though I suppose we do need to at least practice how to handle arguments with people who do perceive them this way).