You should be able to change the IP address for a virtual host as well as change an IP-based virtual host to a name-based virtual host and vice-versa. I had an SSL site as an IP-base virtual host that I was changing to a regular site. There was no way to do it through Virtualmin. I had to do it manually. Another thing about that is ProFTPd can share IP's. Why does Virtualmin say it can't? You should be able to change the IP for ProFTP to a shared IP.