If you receive Error 50 DISM does not support servicing Windows PE with the /online option in Windows 8, then this post may help you.

The DISM.exe tool lets you mount a Windows PE image and add or remove packages, drivers, and language packs in the same way you would any Windows 8 image using the appropriate driver, package, or international-servicing commands.

But Windows PE profiling functionality has been removed now. The base syntax /Image and some of its options cannot be used with an online, running version of Windows PE. You must now specify a Windows PE image using the /Image:<path_to_image_directory> option.

For a full read on how each Windows PE servicing option can be used on a Windows PE image visit TechNet.