Rewriting history has absolutely nothing to do with this. In a VCS that doesn't allow this, I could just hand out repo1 and repo1+malicious-patch. In both cases

Rewriting history has absolutely nothing to do with this. In a VCS that doesn't allow this, I could just hand out repo1 and repo1+malicious-patch. In both cases (as with git as well), I can detect this by comparing hashes.