Hi, @Kal
You can use this command below to find out the particular/specific text from all the files:
$ grep "search_string" /path/to/dir
Then you can use this command below to rename that specific text in all the files:
$ grep -rl old string - / xargs sed -i -e 's/old string/new string/'
Try this, it should work. Just let me know if it works.