I just flagged a post for moderation, but afterwards realized I was being a bit precious and wanted to take it back.
But it seems that what has been flagged cannot be unflagged…
Just flag it again and explain what happened. The same people that get the flag report will get your subsequent report as well. At least that’s what I’ve always done. Similarly, I’ve flagged or reported posts/threads just to give the mods a heads up about something. Flagging a post doesn’t do anything automatically*. Think of it more like a PM to a mod that includes a link to the post.
You could PM the mods to explain it, but that seems like more work than it’s worth.
Another option, if you’ve posted to the thread in question, is to flag one of your own posts and explain the situation.
*Unless enough people do it, then I think the software is set up to automatically hide or lock the thread until a mod can review it.
Thanks, but I can’t reflag a post; for me that option disappears.
I forgot about that. Flag your own post or someone else’s or scroll down to the bottom and flag the thread and use that to explain what’s going on.
Your flag is a message sent to the moderators. You can find it in your profile, and reply to it.
Yeah, your flag starts a message thread visible to you and the moderators (though the moderators can make it private to moderators only.) Usually a moderator replies to it eventually, sometimes with a form message, sometimes otherwise; you can reply to that reply, which will show up in your notifications.
Or you can go to your profile, and look in your messages; as @Pleonast said.
So I don’t think you can unflag it exactly; but you can explain that you’d like to.
Yes. I have had discussions after a flag with moderator.
Your flag may illicit no more than a “we’re looking into it” message back.
Don’t worry about it. They get junk flags all the time, I’ll bet.
Thanks, yes as soon as I got the email message I replied saying I’d prefer to take it back 
Is there a way to un-post a thread about un-reporting a post? I’d open another thread to ask but that could start an endless chain of threads on un-doing.
I believe there’s no way to delete posts. They can be emptied of content, within a time period.
Threads can be corn-fielded.
Corn-fielded into forums only seen by moderators…but never deleted.