问题1.“过去式是不是要变成hadn’t+done?”
貌似过去完成时?
这里用的是助动词用法,就像 can-> cannot 一样,不能变成don't can
问题2.have to do -> don't have to do 或者是 don't need to do 都可以.
这里是实义动词.
问题3.need + do = 问题1,所以变为needn't .need to do = 问题2,所以变为 don't need to do
补充一句,你的问题不邪门,只不过,我觉得是你的学习顺序有点邪门...