For those that don't know how to use imagex.exe hopefully I can help clear up some confusion.

For download AIK from Microsoft. http://www.microsoft.com/en-us/download/details.aspx?id=5753

After you install open cmd and go to c:\program files\windows aik\tools\amd64 (if running win7 x64).

I usually put a folder called wim or wim1 in the c:\root to start...

next if you have a wim image extract using the comment

imagex /mount to c:\wim if you want to write to the directory then use imagex /mountrw

make change to your wim

then when you want to unmount use do imagex /unmount /commit c:\wim

command belows

Imagex /?

ImageX Tool for Windows
Copyright (C) Microsoft Corp. All rights reserved.
Version: 6.1.7600.16385

IMAGEX [Flags] /Operation [Parameter List]

  Operation [ APPEND  | APPLY   | CAPTURE | DELETE
              DIR     | EXPORT  | INFO    | SPLIT
              MOUNT   | MOUNTRW | REMOUNT | UNMOUNT
              CLEANUP | COMMIT ]

For help on a specific operation type:
  IMAGEX /Operation /?

Examples:
  IMAGEX /APPEND /?
  IMAGEX /APPLY /?
  IMAGEX /CAPTURE /?
  IMAGEX /DELETE /?
  IMAGEX /DIR /?
  IMAGEX /EXPORT /?
  IMAGEX /INFO /?
  IMAGEX /SPLIT /?
  IMAGEX /MOUNT /?
  IMAGEX /MOUNTRW /?
  IMAGEX /REMOUNT /?
  IMAGEX /COMMIT /?
  IMAGEX /UNMOUNT /?
  IMAGEX /CLEANUP /?

All operations accept the following flags:
  /SCROLL
  /LOGFILE logfile.log

Best of Luck!