It’s possible by pasting this SmartApp snippet. Then Hello Home appears again and you can configure the offline messages (and battery messages). Not sure why this little snippet works, but it does.
definition(
name: "Hello Home",
namespace: "Hello Home",
author: "SmartThings",
description: "Hi",
category: "",
iconUrl: "https://s3.amazonaws.com/smartapp-icons/Convenience/Cat-Convenience.png",
iconX2Url: "https://s3.amazonaws.com/smartapp-icons/Convenience/Cat-Convenience@2x.png",
iconX3Url: "https://s3.amazonaws.com/smartapp-icons/Convenience/Cat-Convenience@2x.png")