The Anapanasati Sutta is not an easy read, although the language itself is quite simple. But its structure is complex and dense, and this complexity raises serious questions about interpretation. The complexity of the structure creates ambiguity. Even the orthodox commentary sees certain passages as capable of different but simultaneous readings, referring to either serenity or insight practice depending on what approach to the practice the practitioner is taking.
We can see how Thich Nhat Hanh can take liberties with the text, but he does so to make the practice explained within it more accessible to ordinary lay people. Are we to assume that this was not the intention of the original compilers? Or can we see the complexity of the sutta as evidence of an attempt to create a discourse that different communities of practitioners could, quite legitimately, read in different ways? In any event, if we are to make sense of this sutta, and extract from it what it has to offer in terms of guidance on the practice, we need to read the structure of the text. It is not just the surface words that convey meaning, but the underlying networks that link the words.