With Personalizer 2 from XDA Developers you can easily change the Operator Name displayed throughout your device to anything of your liking.

Installation is very simple: download Personalizer 2 for free and install it to your Device. You will be prompted for a text to replace the Operator Name on your Device; after you’ve inputted it, that text will remain valid until you change it from within Personalizer 2 (by tapping its icon from the Programs menu) or you uninstall the app, which reverts to default.

Note: If you are having problems with Personalizer 2, you can try Personalizer 3 from PPCGeeks.

Thanks for the tip, @xperiance!