The key to being efficient with keywords and metadata is the same as that for being efficient with applying Camera Raw edits. Look for and select images that need the same treatment, and deal with them all at once.
The only metadata that is editable in the File Browser (or anywhere else in Photoshop, for that matter) is the IPTC metadata. For recurring metadata such as copyright notices, metadata templates provide a very convenient way to make the edits. You can create and save metadata templates from the File Info dialog box—to open it, select a single image to which you want to apply the metadata, then choose File Info from the File Browser's File menu.