How to enable notification history for an application

[David Jarvie]

Can somebody help on how Plasma can be configured to show or hide a specific 
application's notification history, if that application is not already in the 
list of applications shown in the System Settings Notifications list (ie 
Konsole, KDevelop, Spectacle, etc).

Currently, if an application is not already in the System Settings list, the 
user has to select whether to show notification history for ALL applications, 
and cannot as far as I can see select just ONE unlisted application.

I want KAlarm itself to be able to set its default to "show notification 
history", to avoid the user having to know about going to System Settings to 
do this. If possible, KAlarm would also be able to enable or disable showing 
its notification history at any time.

I've set kalarm.notifyrc to contain a DesktopEntry value, but that hasn't done 
anything in itself.

-- 
David Jarvie.
KDE developer, KAlarm author.