“Ngak’chang Rinpoche” and “Ngakpa Chögyam” are two names for the same person. He and his wife Khandro Déchen are the Lineage Lamas (principal teachers) of Aro.
It is the Tibetan custom to be given a new name whenever one has a significant change in religious status. For example, one is given a new name when one takes refuge or is ordained. Generally Tibetans retain their old names as well, and use different ones according to the role they play in a situation.
For example, “Kyabjé Düdjom Rinpoche” and “Jigdrel Yeshé Dorje” are two names for the same great Lama who was Head of the Nyingma (and who was one of the Root Lamas of Ngak’chang Rinpoche). He signed some of his works “Düdjom Rinpoche” and some “Jigdrel Yeshé Dorje,” according to the nature of the text.
It was only recently and by accident that I learned how and when Ngakpa Chögyam received the name “Ngak’chang Rinpoche”—by reading this page.
He has continued to use the name “Ngakpa Chögyam” as the author of his books, to prevent confusion.