AutoCAD Visual LISP / AutoLISP :: Inserting Routine Into Fields

I have a lisp routine:

(defun getLayout (pos / result cLayout layouts^ i len)
; pos = -1 return previuous layout name
; pos =  0 return current   layout name
; pos =  1 return next      layout name
 (cond
  ((zerop pos)
   (setq result (getvar "ctab"))
  ); case

[code]...

which basically returns either the current, previous or next tab name depending on what you call up. Any way to link this lisp to a field? I am doing some plan and profile drawings which contain match lines I would like to have the match line text automated. For example if I'm on layout called PP02 there would be two match lines in the drawing one would read MATCH LINE PP01 and the other would read MATCH LINE PP03 this lisp routine returns the correct variable but how do I loink this to a fiels?