Veritas Alarm 8 Designated Entry Point?

I have a veritas 8 alarm in my house, it is a new property and I want to change the settings for it as the Designated Entry Point is on the front door sensor, unfortunately due to the layout of the property we use the back door as the main entrance to the house, and therefore when we set the alarm it goes off as soon as we enter the back door. Is there any way of changing the Designated Entry Point to the back door sensor as the electrician who installed it says it can't be done and I'm not sure thats right!! If someone could give me some pointers I'd be most grateful!!