Generally it is not acceptable (see relevant MSE question at Should I use existing questions to "ask new ones" when in a question ban?). If there has been pretty much any significant activity on the previous question (comments, answers, votes), changing the question just renders all that previous activity obsolete and, in the case of votes, arguably straight-up fraud (any positive votes would NOT have been for the new question, giving it an unfair advantage over having been posted anew).
Right now, taking action on that question would be counterproductive, since it currently has significant activity taken on it due to the current form (and had not had significant activity in the previous form): The copy-pasted answer had already been deleted before the question was changed (and wouldn't be welcome on the site anyway), and the only votes cast on it were for the question it's asking now. Deleting it or rolling it back now would also render Medi1Saif's efforts in his answer completely irrelevant, effectively wasting his time and hurting his reputation unnecessarily.
However, this should be considered an exception; if the post had had even one upvote or one viable answer from its earlier form(s) I would've rolled it back instantly, new answers or no. Encouraging this sort of behaviour risks well-intentioned contributions getting wiped out during cleanup (moreso than answering poorly-written or unclear questions in general), which is just not fair to the people volunteering their time to help. If you do see this sort of thing in the future, don't hesitate to roll it back and warn the poster before other users see it and unwittingly contribute to the wrong post.