(map (vec "SUCCESS") [0 5 6])
which certainly isn't Elisp.
My first attempt at Elisp is
(mapcar (apply-partially #'aref "SUCCESS") '(0 5 6))
which does the trick but outputs the results as integers
(83 83 83)
because that's how Emacs represents characters.
If we want to print out the actual S's we need to wrap the above in some extra code
(mapcar #'char-to-string (mapcar (apply-partially #'aref "SUCCESS") '(0 5 6)))
("S" "S" "S")
What we really need here is something like the Common Lisp
char function that outputs the actual characters but, of course, Emacs can only do this my making strings. On the other hand, CL lacks the nice currying function
apply-partially so I don't see a nice succinct solution in it either.
Update Noam has a much better solution in the comments.