I think you don’t need a script to do this. What you need is GREP search/replace. I’m not expert in GREP, but it seems that the following does the job:
Find what: (?<=n)(o)\b
Change to: leave empty
Change format: select superscript (Basic Characters Formats > Position)
Better to specify a word beginning as well to avoid Zeno and the like:
Are you sure that the word "no" (as opposite to "yes") does not occur in the 300 pages?
You probably have to check each replace anyway. Try to limit the find results as tight as possible:
Maybe there must always be a space+digit after the "no" that needs superscripting.
Maybe specify to search for whole words only.