Alternative to the reject and request rewrite approach, which may not work in the corporation environment. You schedule a really long video call with the offending person, with the agenda politely describing that for such a huge and extensive change, a collaborative meeting is required. You then notify your lead that new huge task has arrived which will take X hours from you, so if he wishes to re-prioritize tasks, he is welcome. And then if the meeting happen, you literally go line by line, demanding that author explain them to you. And if explanation or a meeting are refused, you can reject RP with a clear explanation why.