I tried replacing notifications with other sounds for Display Off and other updates, but now I get both the annoying Life is Good and my quiet choice (Sprout). I attached the phone to my laptop and looked for the Life is Good notification sound, but I cannot find it to delete it. I only found the 2+min music file.
System notification files cannot be deleted. They are OS-protected. The display off and notification sounds are in sounds and notifications under Notifications and Advanced settings. Screen off sound is default to a very short tone and I can't see a way to make that any other sound. Where or when are you hearing "Life is Good?"