Changing device configuration to display non-circular launcher icons According to this article, an Android device's "system framework decides whether or not to return either the regular icon or the round icon to the launcher."  "When a launcher requests an app icon, the framework returns either android:icon or android:roundIcon, depending on the device build configuration."

Is it possible to alter the device build configuration to change the default icon display to non-circular?

I'm on a stock, non-rooted Nexus 5X.
For a non-rooted device, it's not possible as far as I've seen, as it's totally under control of OEM as implied in this Android developers documentation. But otherwise, it's possible if one can edit config with the value of config_useRoundIcon to false.

Just for experimenting, you can decompile the framework-res.apk and change the above-mentioned value in bools.txt and recompile the apk and push the apk into the device.