Windows – Reg.exe Offline registry edit

Ok I want to edit an offline registry entry from WinPE, if I am booted into the OS (32bit) the reg key is:

hklm\system\currentcontrolset\services\mountmgr\noautomount

So I boot into WinPE and run my batch file to do these commands:
(Tried on 32bit and 64bit)

Echo Loading Regestry Hive
reg Load HKLM\temphive H:\Windows\System32\config\SYSTEM
pause
Echo Import the reg
reg add "HKLM\temphive\system\CurrentControlSet\Services\MountMgr" /v "NoAutoMount" /t REG_SZ /d 0x1
Reg IMPORT z:\Restore\NoAutoMount.reg
regedt32 /s z:\Restore\NoAutoMount.reg /reg:64
Pause
Echo Query the key
reg query HKLM\System\CurrentControlSet\Services\MountMgr /s
pause
Echo Unload Registry Hive
reg unload HKLM\temphive 

Registry file:

Windows Registry Editor Version 5.00

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\services\mountmgr]
"DisplayName"="@%SystemRoot%\\system32\\drivers\\mountmgr.sys,-100"
"Group"="System Bus Extender"
"ImagePath"=hex(2):53,00,79,00,73,00,74,00,65,00,6d,00,33,00,32,00,5c,00,64,00,\
72,00,69,00,76,00,65,00,72,00,73,00,5c,00,6d,00,6f,00,75,00,6e,00,74,00,6d,\
00,67,00,72,00,2e,00,73,00,79,00,73,00,00,00
"Description"="@%SystemRoot%\\system32\\drivers\\mountmgr.sys,-101"
"ErrorControl"=dword:00000003
"Start"=dword:00000000
"Type"=dword:00000001
"NoAutoMount"=dword:00000001

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\services\mountmgr\Enum]
"0"="Root\\LEGACY_MOUNTMGR\\0000"
"Count"=dword:00000001
"NextInstance"=dword:00000001

Now if I boot to the OS and set this registry entry it works, but if I try to update it ofline it does not. I know if I load

HKLM\temphive

That's what I need to edit right? But if I do then boot into windows the registry key is not there.
What am I doing wrong? and would it be different for 64bit over 32bit?