[Garkin]

There is needed a bit more code to make it work. I think the best way is to ask Sideshow to add it...

If you want do all the job, you will need to add your new notification type to the Power.lua, Constants.lua, Notification.lua, Menu.lua, Defaults.lua and to the localization files.

If you just want to make it somehow work with no settings, you will need to make at least the following changes:
changed parts of Core\EventViewers\Notification.lua:

--lines 1 - 42 from the original code here
    elseif (notificationType == 'COMBATCLOUD_NOTIFICATION_TYPE_EXECUTE' ) then
        color = {1,0,0,1} --red color, format is {r, g, b, a}
        text = self:FormatString('%t!', { value = value, text = 'Execute!' }) --displayed text will be "Execute!"
--rest of the original code (lines 43 - 76) here

changed part of Core\EventListeners\Power.lua:

--lines 1-10 from the original code
    self.executeWarning = false
--lines 11-35 from the original code 
    if (unit == 'reticleover' and powerType == POWERTYPE_HEALTH) then
        if not self.executeWarning and (power / powerMax) < 0.25 then --target's health is below 25%
            self:TriggerEvent(CombatCloudConstants.eventType.NOTIFICATION, 'COMBATCLOUD_NOTIFICATION_TYPE_EXECUTE', power)
            self.executeWarning = true
        elseif (power / powerMax) > 0.35 --target's health > 35%
            self.executeWarning = false
        end
    end
end --line 36 from the original code