Yes, replace
Code:
 var %word2 = $iif($read(replace.txt,s,%word1),$v1,%word1))

with one of the following

1) Word must end with the item being searched (ie: searching for op would also catch stop)
Code:
 var %word2 = $iif($read(replace.txt,w,$+(*,%word1)),$v1,%word1))


2) Word must start with the item being searched (ie: searching for op would also catch ops)
Code:
 var %word2 = $iif($read(replace.txt,w,$+(%word1,*)),$v1,%word1))


3) Word can occur anywhere (ie: searching for op would also catch stops)
Code:
 var %word2 = $iif($read(replace.txt,w,$+(*,%word1,*)),$v1,%word1))


NOTE: These will replace the ENTIRE word, not just the portion of the word that matches