Something like this?
No error checking!
(defun c:myattedit (/ ss)
(if (setq ss (cadr (ssgetfirst)))
(if (> (sslength ss) 1)
(prompt "\nError, too many selectd.")
(progn (initdia)
(command "attedit" (ssname ss 0))
(princ)
)
)
(progn (initdia)
(command "attedit")
)
)
)