Cue sheet files (and also lyrics files) can be edited. Get the complete file pathname (you can get this via the 'Edit Item' box of the music database), open an text editor such as Wordpad or Notepad if the file extension is TXT or HTML; or open an editor such as MS Word if the file extension is RTF. Make the necessary changes, then save the file (with the same name).

You can edit an HTML or TXT cue sheet via the 'Music Database - Edit Item' window. Just click on the edit toolbar button (with the 'pencil') icon to the right of the Cue Sheet filename.