Flikky's Textbox Tools
Textbox Tools allow you to convert the textbox SAY lump into plain text and back again.
A similar feature is built in to the latest versions of CUSTOM. In the "Edit Text Boxes" menu look for the "Import" and "Export" menu options.
The plain text format used by Flikky's text tools is different from the plain text format generated by the Export tool, so the files are not directly compatible.