The software is for personal and business use, meaning you don't need a registration code to use its core features. The "registration code" requests you may see online typically refer to unofficial attempts to unlock non-existent "Pro" features or to remove a nag screen in modified versions.
If you prefer tools that are entirely open-source or have different feature sets: Free IP Switcher - Free download and install on Windows Free Ip Switcher 3.3 Registration Code