Make it so that you can only change one or two characters, and make every edited tweet have a prominent button to see the original tweet. Maybe make it so that you can’t change links, images, or other media.

You're still inviting trolls.

"What an amazing pitch!" becomes "what an amazing witch!" (or worse). Well-known users would hate it because they'd be mocked for stepping into the troll trap.

HN is, how should I say, not Twitter in any sense of the platform. At all.

HN also has a stricter set of community guidelines (which aren't in themselves all that strict to start with), more heavily moderated, and a generally well-educated, mature-minded user base that is generally appreciative of these two elements.

And way less users.

Yep, way fewer users. And what spam accounts exist get squashed pretty quickly. If HN ever releases statistics on the number of users, I'm sure they have more dignity than to include spam and bot accounts — which is, I'm sure, the majority of Twitter accounts.