[reg.exe]C:\>reg add /?

REG ADD KeyName [/v ValueName | /ve] [/t Type] [/s Separator] [/d Data] [/f]

KeyName [\\Machine\]FullKey
Machine Name of remote machine - omitting defaults to the
current machine. Only HKLM and HKU are available on remote
machines.
FullKey ROOTKEY\SubKey
ROOTKEY [ HKLM | HKCU | HKCR | HKU | HKCC ]
SubKey The full name of a registry key under the selected ROOTKEY.

/v The value name, under the selected Key, to add.

/ve adds an empty value name (Default) for the key.

/t RegKey data types
[ REG_SZ | REG_MULTI_SZ | REG_EXPAND_SZ |
REG_DWORD | REG_BINARY | REG_NONE ]
If omitted, REG_SZ is assumed.

/s Specify one character that you use as the separator in your data
string for REG_MULTI_SZ. If omitted, use "\0" as the separator.

/d The data to assign to the registry ValueName being added.

/f Force overwriting the existing registry entry without prompt.

Examples:

REG ADD \\ABC\HKLM\Software\MyCo
Adds a key HKLM\Software\MyCo on remote machine ABC

REG ADD HKLM\Software\MyCo /v Data /t REG_BINARY /d fe340ead
Adds a value (name: Data, type: REG_BINARY, data: fe340ead)

REG ADD HKLM\Software\MyCo /v MRU /t REG_MULTI_SZ /d fax\0mail
Adds a value (name: MRU, type: REG_MUTLI_SZ, data: fax\0mail\0\0)

REG ADD HKLM\Software\MyCo /v Path /t REG_EXPAND_SZ /d ^%systemroot^%
Adds a value (name: Path, type: REG_EXPAND_SZ, data: %systemroot%)
Notice: Use the caret symbol ( ^ ) inside the expand string[/quot]