I started a similar thread earlier about wanting to be able to customize notifications: Custom Zigbee Notification Animation (Loop).
It never really got much traction. But I suspect that some of the issue is that we still don’t have any way to contribute to firmware development. See this discussion: Use the community to help with development - #12 by wbyoung.
And finally, maybe a bit off topic, but I just got this integration into HACS which I’m using for controlling notifications across multiple switches in my house simultaneously: Lampie: Notifications on Multiple Switches for Home Assistant.