Hmm ... I wonder if they have an edit limit where old edits get erased if you keep editing, sort of like that trick someone came up with years ago for pinging the credit bureau so many times so that eventually your credit looked better since old items were erased or not considered for your credit score ... or something.
It's called "bumpage" or "B*" on forums. People were leery of using the word back in the day because they thought the bureaus might catch on. It doesn't work anymore.
This is the case with many other online platforms (such as reddit) in that the original content of a post is still reachable if it was deleted, so a common method is to "scrub" edit your posts then delete them.
However at Facebook's size, and given they're known for 0 privacy, they likely track all changes anyway.
Reddit doesn't actually store the history of your edits, only that you edited it (which is why, when you scrub reddit history, people recommend editing it because then your posting is gone except for say a backup). Facebook, however, allows you to see the history of posts so if someone edits it you can see what they originally posted.
I don't think editing a Facebook post first would have the desired effect.
I'd be much less confident, considering that they explicitly save and make public post's edit history.