LeanLord Your boss told you not to apply an upgrade that contains security and bug fixes, specifically the bug you're encountering now? ?
Technically, as an upgrade is just replacing the PHP files then that's the same as the manual solution you're looking for, but I know how stubborn bosses can be at times ? You might be able to find a pull request in Github that sorts your problem, although this is effectively just a partial upgrade. I'm afraid I don't know how to sort this manually, although if you look through the files you might be able to find the strings somewhere. I'd advise against doing this though.