You'll see from the earlier-linked thread that Pages has problems running AppleScripts over large amounts of text -- and it looks like you've enough on every page that even taking it one page at a time is hitting those limits.
As @Airy says, if you want to replace all "(" and ")" you should be able to do it within Pages with just two global Find and Replace operations -- it isn't even worth writing a macro. I put screen shots of the two (tested) dialogs in my previous post.
If you want to only replace some -- say, put Returns before and after (to Ruth) but never around (laughter) -- you are going to have to get creative. If it is a limited "exclusion list" I'd do something like:
- Find and Replace all the "(" and ")" around the exclusion list terms with "####" and "$$$$", respectively
- Do the above two Find and Replaces on all remaining "(" and ")"s
- Find and Replace "####" and "$$$$" with "(" and ")", respectively
If there's a lot of these it wouldn't be too difficult to put the list into a KM variable and drive the dialogs with a macro.
Anything more complicated and you are probably better off exporting to Word or LibreOffice, using their regular expression supporting Find and Replaces, re-importing the result back into Pages.