Great. If you didn't validate that push notification is working, connect to your hub, then go to Devices and click on your mobile device. Type and send a test notification to confirm the push notification is working. After that, go to Apps and create a new Basic Rules rule - when door unlocked, send push notification to your phone.
Try logging out and back in on your mobile app. To log out go to Settings tab. When you log back in, select the same device. After logging in, send another test message to your phone.
Yes, anything is possible, just not with Basic Rules app. To use a preset variable you will need to install an app called Notifications. Follow the link to learn more.