How to disable warning messages? On Android 4.3 un-rooted, is there a way to disable all the annoying warning messages that pop up when you enable Airplane Mode / disable Airplane Mode / raise the volume too high / etc? 

Apparently the Xposed mod allows to do this tweaking but I have found no solution so far for an Android device that hasn't been rooted.
You can use Tasker with the AutoInput plugin to detect the pop ups and close them. 

Or you can use Tasker to turn Wi-Fi, GPS etc on/off. You may have to add Tasker as an admin app for it to control the GPS and some other functions.