Sure. Like this?
Command RMT.
It also works for TEXT objects. If you don't want this, replace (cons 0 "TEXT,MTEXT") by (cons 0 "MTEXT")
(vl-load-com)
;; RMT for Replace Mtext
(defun c:rmt ( / ss newtext i)
(princ "\nSelect TEXT/MTEXT elements: ")
(setq ss (ssget (list (cons 0 "TEXT,MTEXT") )))
(setq newtext (getstring "\nNew text: " 1))
(setq i 0)
(repeat (sslength ss)
(vla-put-textstring (vlax-ename->vla-object (ssname ss i)) newtext)
(setq i(+ i 1))
)
(princ)
)