>I would like to be able to make one of my own EXECs that resides on the
>LISTSERV 191 disk, to run when invoked by a command received by LISTSERV,
>to execute as part of its functions, a LISTSERV command.  Can I do this
>by having the EXEC call LSVCMD?
 
Yes, in fact LSVFOR EXEC does exactly that to implement the "FOR" command.