Many Windows system files, registry keys, and services are owned by the SYSTEM (a.k.a LocalSystem) account, which has a high privilege level. If you need to modify a registry key owned by the SYSTEM account, there are at least two options.
The first option that comes to your mind is to take ownership of the corresponding registry key, assign yourself Full Control permissions. Once the registry key or the values are updated, revert the permissions and ownership to SYSTEM.
There is, however, an easier option. You can run the program — e.g., the Command Prompt or the Registry Editor under the SYSTEM account directly and update the registry values.
This article lists 7 different methods using which you can run programs under the SYSTEM or LocalSystem account in any version of Windows, including Windows 10. You can also add a Run as SYSTEM right-click menu option for .exe files.