A safe API would look a lot like Windows' GetEnvironmentVariable and SetEnvironmentVariable
https://learn.microsoft.com/en-us/windows/win32/api/winbase/...
https://learn.microsoft.com/en-us/windows/win32/api/winbase/...
https://learn.microsoft.com/en-us/windows/win32/api/winbase/...
https://learn.microsoft.com/en-us/windows/win32/api/winbase/...