Normally, we would say ‘changed’ here instead of ‘altered’. Normally, something stated is altered. His appearance was so altered that I barely recognized him. I scarcely recognized him due to his altered appearance.

No, it's fine as it stands. There could be an optional comma after the word "much," "He had altered so much, I scarcely recognized him." My guess is that you are wondering about that. It is completely optional, it isn't needed. Putting in the comma even seems old-fashioned. Today it would be more common to leave it out. Some writers might add the word "that" after "much," "He had altered so much that I scarcely recognized him," but, again, it's optional. Language changes, there are slow changes that occur over decades and centuries. In English there is a definite trend to use less and less punctuation.

There seem to be no missing elements.