yes should be all possible, some quick examples ( not all, but if you search enigma2 / enigma2-plugins or such you should be fine )
standby:
config.misc.standbyCounter.addNotifier(self.StandbyCallback, initial_call = False)
change channel could be monitored by the evStart, maybe you need to check if it's a live channel or media but thats up to you
self.__event_tracker = ServiceEventTracker(screen=self, eventmap=
{
iPlayableService.evStart: self.evStartCallback
})
for recording should be simular to this, please check it
volume you probably need to hook to the volume keys ( see i.e. the multiquickbutton or something like that )
also the plugin needs to autostart ( so it is activated when enigma2 starts ), find some examples, they are plenty
hope this helps...