You should be able to edit a post until the first payout. When the payout has occurred, you can't edit it anymore.

I'm not sure but I don't think there is a way to delete anything from Steemit.com (at least it's impossible to delete anything from Steem blockchain – it's a blockchain, after all).

Usually it's not a good idea to post same thing many times. Other people might think that you are just trying to fish more upvotes by continuous posting.

Your explanation seems plausible so I removed my downvote.