If you need to manipulate registry data from another user, you may be out of luck because HKEY_CURRENT_USER always points to your own user data. However, you can manually load a user hive like this:
reg.exe /load HKU\Testuser c:\users\tom\ntuser.dat PS > dir Registry::HKEY_USERS\Testuser\Software
This will load Tom’s registry settings into HKEY_USERS\Testuser and once loaded, PowerShell can then access and even manipulate that data.