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Editing is not strongly discouraged, and adding a disclaimer is not rare.

Editing in general no, changing the answer is. You get rebuked and told to post your own.

Yep, and then the better answer will sit at the bottom of the page, while the older one continues to be seen and gathers more upvotes.

I think there is a critical mass after which the site's focus changes from creation to protectionism, and then it becomes stagnant.