Still won't solv. I will keep to receive messages from people that access the old topic.
The problem here is that IPS untied the support topic from the file years ago, so the dev creates the topic if he wants. In a "regular" usage, changing the author in Downloads, will also change the topic author.
Even locking the old topic (support will be given in the new one), relevancy will show the old topic in search results, for example.