The notification sound itself when arming, disarming or selecting home on the alarm panel cannot be changed, however you can disable the sound by following these instructions.
1. On the Smart Life app select the Gen 2 Device
2. Then select 'Setting' located at the bottom
3. Where it says Arm/Disarm push, on = green, toggle the switch to off = Grey
Now when you arm, disarm or select home on the alarm panel, you will not receive a notification sound on your smart phone.