Carrier Vanity Name is a very simple app to change the carrier names on unrooted Android devices.
The changed names will persist through reboots. To revert them back, click the reset button in the app.
The app can also override the ISO country code of your SIM card. This can be useful to spoof your location to some region-locked apps like the Pixel Thermometer.
The app uses Shizuku to achieve this using carrier config overrides. This method was inspired by Kyujin Cho's pixel-volte-patch, which uses the same method to enable VoLTE on some Google Pixel and LG devices.
WARNING: Anything using Shizuku might potentially cause harm to your device (and the data on it). I'm not responsible for any damage that might be caused by this app. You have been warned.