This brings up memories of when moot messed with /pol/. He turned off the spam prevention scripts and captcha, made every post look like a doubles post, and let an audio recording of cuck porn play on the board page. That was sort of expected from moot though and it was 4chan after all.

Well, yes.

but he didn't mess with any of the content of any messages.

If he did, the entire chan would have gone up in flames.

The content was subject to a large amount of wordfilters at the time, which would alter half the posts.

...but those were public. It's one thing to have a computer run search and replace on every post in the board. It's quite another to have a mod specifically edit your post, making it look like you said something you didn't.

I've been wondering about exactly that - would the perception of this be so negative if spez had inserted javascript to rewrite the messages on that subreddit instead?

No, because that would rewrite everybody's messages. And it would be noticed immediately, so it wouldn't even matter, practically.

In what way is it an abuse of the system?

They arent democrats