The specific command in AutoLsip that you're looking for is vl-string-subst. This however stops after it finds the first match in a string. If you want to go through the entire string and substitute every match, then Lee Mac has a simple solution for this problem. You'll probably need to add vl-load-com somewhere in the script to use vl-string-subst.
vl-string-subst documentation: Link 1 
lv-load-com documentation: Link 2 
- Lee Mac's solution: Link 3
 
;;--------------------=={ String Subst }==--------------------;;
;;                                                            ;;
;;  Substitutes a string for all occurrences of another       ;;
;;  string within a string.                                   ;;
;;------------------------------------------------------------;;
;;  Author: Lee Mac, Copyright © 2011 - www.lee-mac.com       ;;
;;------------------------------------------------------------;;
;;  Arguments:                                                ;;
;;  new - string to be substituted for 'old'                  ;;
;;  old - string to be replaced                               ;;
;;  str - the string to be searched                           ;;
;;------------------------------------------------------------;;
;;  Returns:  String with 'old' replaced with 'new'           ;;
;;------------------------------------------------------------;;
(defun LM:StringSubst ( new old str / inc len )
    (setq len (strlen new)
          inc 0
    )
    (while (setq inc (vl-string-search old str inc))
        (setq str (vl-string-subst new old str inc)
              inc (+ inc len)
        )
    )
    str
)