My text is composed of the "privacy policy" and the "terms and conditions" of a website.
I want you to modify few words and few sentences (without changing the meaning of the text, obviously)
That's sort of illegal and shady. As far as I know, company's terms and conditions are usually drafted by a legal authority like a lawyer. You can't simply copy someone's terms and conditions and modify them. That simply shows you're not serious about your business. Who knows what else you could have copied from that site?
I'm afraid you're doing the right thing. He could be modifying the text to look legitimate. Usually when busting fake ICO's, I check their terms and conditions with a plagiarism checker to see if it's ripped off somewhere. I wouldn't advice going forward with this one.
Rewriting is completely legal so long as it's not simply a 100% rewrite, when originality, creativity and effort are applied it becomes something new, that is unless the entire text is copyright, which is unlikely.