Sometimes I need to fiddle with a registry setting normally under HKEYCURRENTUSER, but that points to your own hive. When you need to change another user's registry whilst being logged in on a terminal server, you cannot load the hive file ntuser.dat as it is already loaded. For that issue the following command in cmd.exe:

wmic useraccount get name,sid

Then use the SID to locate the user's hive under HKEY_USERS.