WACUP already provides 2 ways to edit metadata. Right-click on a file listed in the media library or the playlist editor and select the "View file info..." command or the "Edit metadata for selection..." command in the playlist editor.
The "View file info..." command lets you see, edit, and/or add metadata tags for supported file formats that store metadata tags within the files themselves. This command works best when working with the supported file formats one file at a time.
The "Edit metadata for selection..." command lets you see, edit, and/or add metadata to media library file records for supported file formats that may or may not store the metadata within the files themselves. This command can optionally update the tags for supported file formats that do store metadata tags within the files themselves. This command can be used to make the same change(s) to a group of file records and within a group of supported files at one time.