Yes, you can use Rebex Ftp client in explicit mode with custom ports, just do:
int customPort = 29;
client.Connect("server", customPort, SslMode.Explicit);
The Rebex Ftp client will work if server will be properly configured to use the special port. Please note that usually port 21 is denoted for FTP with explicit (or none) SSL/TLS mode.
I am sorry Rebex cannot provide you with details for configuring TLS/SSL at the server, as we only provide support for the Rebex Ftp client. Maybe try to google how to enable the TLS/SSL for your server...? It also depends on the exact FTP server that you use.