On a hardcopy terminal, change mode operates this way:

 When you enter change mode, EDT displays the current line on the
 terminal. The cursor position is marked by bracketing the character on
 which the cursor is positioned.  EDT will then prompt with the
 characters:

     C*

 In response, you type a series of nokeypad mode commands terminated by
 pressing return.  EDT will execute the commands and type the current
 line.