Installing .apk as system app directly (with root) I'm wondering is it possible to install .apk file as system app directly (with root)? Without converting user app to system app.
You can simply copy the apk (its name not relevant) into /system/app or /system/priv-app, set the appropriate permissions (rw-r-r, root:root) and then do a reboot. That's it. 

Works well on Android 6.0.1.