Setting metadata values for multiple assets can easily be done using the Media Box.
- Open your Media Box and select "View" from the menu.
- Click "Select all"
- Press the "Edit" icon
Select any of the available metadata field checkboxes and fill out the new content values. There are three different modes of applying changes, Overwrite, Append or Clear Field.
Caution! There is no way to undo a multiple edit. Please thread carefully.