Can I still delete the messages that I sent to a wrong person?

If you're talking about email or text messages you've sent to the wrong person, yes, you can delete them off of your device. However, that doesn't undo the mistake. Whoever you sent the message to will still get it.

Are you talking about posts you make here on the ASC?

If so, you can't. You have 15 minutes to edit a post, but there is no way to delete it.

Also, the message isn't sent to someone. It is just listed as a reply to that person.

Reply to your own post and explain that you intended to reply to someone else, if it really needs to be explained.

If you are actually talking about text messages sent via Messages, I'm not sure that is possible, either.

With this new ASC format, I can't tell which you mean.