Just to expand, it is recommended to copy ISO content as is inside a writeable folder for editing.
Then add that entire folder to NTLite Source page, and load the image from the UI.
Thus when done you can even automate to create an ISO on the Apply page, no need to edit WIM files in isolation, nor is it recommended.
Dynamic update for example, which is a Windows setup update, requires ISO content to be applied properly.
Also Post-setup automation to be external to the WIM image for easier installer updating etc.