Library /sys$common/syshlp/dtehelp.hlb SET, DTE, /COMMAND  *Conan The Librarian (sorry for the slow response - running on an old VAX)

       /COMMAND=character

    Selects the command character.

    You can select the command character from any ASCII character
    between @ and z, except C, M, Q, S, Y or the left bracket ([).
    You cannot select a character currently defined as either the
    break character (see the /BREAK Subtopic) or the escape
    character (see the /ESCAPE Subtopic).

    By default, the command character is the commercial "at" sign
    (@).