Legal Question in Intellectual Property in Texas

Convoluted multi-part question, but generally no, you can't force the website to remove a post if they do not want to remove it and you cannot assert a copyright on the post effectively to control its use. Only if you obtain prior agreement of the host that you retain copyright and can take the post down anytime are you going to be able to force this, and even then it might take litigation to get a court order, which generally will cost enough you won't pursue it. I never recommend such suits. There are more effective ways to address the issue, whatever it is about the post that bothers you now, than making some half-baked ineffective copyright claim. If you call, for a fee, I can advise you of alternate strategies my clients and I use in these situations, but I don't give those for free and then why should anyone pay for the advice?