The idea of the popup is good. In fact, I've seen that on another forum which basically prohibits the user from reporting the same post again while allowing reports from others.
It is not good if completely prohibit re-report on the same post.
After reporting one post for the first time, there should be chances for us to find more details of that case and we need to re-report it with more details/ references.
I remember a few times that I've reported in the past, I had come across new information which provided a better explanation to why I was reporting. Although, I'll admit this isn't something which props up often
As of now, the forum does not give us option to edit our reports and automatically resend/ reallocate re-edit reports to the same moderators who previously receive our first report on the same post.
Due to this, allow re-report a same post (by a same reporter) is good but it need support tool like a pop-up message.