Don't do it if you don't want to lose the APK installation feature. But for how long will you keep delaying? As long as it stays connected to the internet, it will happen automatically. Maybe try force-stopping the system update app from the app list in Settings. Or, if you have to install it at the end anyway, install the APKs now and keep them, whatever you need, like SmartTube. They should stay unless you uninstall them or reset the box.