Yes you can change the SMTP port in the gwia.cfg file by using the following switch: --smtpport 25
I don't know how well this will work though!
You can change the port in ConsoleOne to match what you are doing in the gwia.cfg file. Once set and GWIA has been shutdown entirely and then restarted you can test by using telnet to your IP address and specifying the new port number.
Ensure that under the Network settings your GWIA is set to "Bind Exclusively to TCP/IP Address".
Then check what ports your GWIA is running on:
gw12:/ # netstat -plan | grep gwia
tcp 0 0 10.11.41.102:25 0.0.0.0:* LISTEN 18238/gwia
tcp 0 0 10.11.41.102:9850 0.0.0.0:* LISTEN 18238/gwia
tcp 0 0 10.11.41.102:7102 0.0.0.0:* LISTEN 18238/gwia
That should give you an indication of whether it is binding on port 25 (see above) or on your uniquely specified port.
Let us know how it goes.