Changing device configuration to display non-circular launcher icons
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.