I edit all my posts before I publish them – I look for poor grammar, me rambling on (something which I’m terrible for) and things like typos, although some do still get through. I think that kind of editing is fine.
But when it comes to opinion pieces, I don’t think they should be edited. Yes, you should (in my opinion) check the spelling/grammar before posting, but I don’t think you should go back and edit your opinions retrospectively if they change.
Kev Quirk

Kev speaks my mind.
At almost 25 years ago, my blog’s ancient, and covering more than half my life it inevitably includes posts that I feel don’t accurately reflect me any more (or, perhaps, didn’t reflect me well even when I wrote them!). My approach has long been that it’s okay to go back and modify a post to:

Correct spelling, punctuation, and grammar, or improve readability without changing the meaning.
Add content (in a clearly-marked way) to improve context, update information, or prepend/append hyperlinks to updated information.
Make changes that protect an individual (e.g. removing the name or photo of somebody who doesn’t want to be identified).

But like Kev, to me it just doesn’t seem right to change opinion pieces after your opinion changes. I’m happy to write a retraction and link to it from the original, but making-out like I never said those things in the first place seems disingenuous.
Kev links a disclaimer from his older posts; that’s an interesting idea that I might adopt.