说 a changed man 完全可以的。如：
When he did recover at last, he was a changed man. 病过去之后，他几乎变成另一个人。
As set forth, he was a changed man from that moment.  如前所述，自那时起他就变成了另外一个人。
又如下面一句摘自《柯林斯高级英语词典》：
He has been a changed man since his divorce. 他离婚后像是变了一个人似的。
下面一句摘自《牛津英语习语词典》：
Since the attack he’s been a changed man. He’s nervous of his own shadow and doesn’t like to go out alone at night. 自从那次袭击过后他变了个人，变得非常胆怯，晚上也不愿意独自出门。