Recursive Open

NameChanger's open dialog offers two ways to add selected folder contents.
To reveal these options you may need to click the Options button on the bottom left of the open dialog.

Open folder contents

Checking the "Open folder contents" option will take just the top level items in whatever directories you select.

Recursive

If you check "Open folder contents" AND "Recursive" then it will add all the files found in the selected folders and nested subfolders. No folders will be added, only files within those folders.