Lang’s (cubibobi) questions:
(1) Yes.
(2) I am not certain that those commentaries were actually written or just composed (just like the rest of the Tipitaka). I have revised that in the post as:
“.. Furthermore, three commentaries were composed in Pāli during the time of the Buddha. Per the Sinhala version of those three commentaries, one was the work of Ven. Sariputta and the other two attributed to Ven. Mahākaccāna (or Mahākaccāyana.)
#3, #4: Yes. Those certainly qualify as “distorting Buddha Dhamma.”
– I am not sure whether they qualify as anantariya kamma. But it is a serious offense.
For example, “AN 2.25” is a short sutta that says: “Dveme, bhikkhave, tathāgataṃ nābbhācikkhanti. Katame dve? Yo ca neyyatthaṃ suttantaṃ neyyattho suttantoti dīpeti, yo ca nītatthaṃ suttantaṃ nītattho suttantoti dīpeti. Ime kho, bhikkhave, dve tathāgataṃ nābbhācikkhantī” ti.
Translation (to provide the idea): “Monks, these two people slander the Tathagata. Which two? One who briefly explains a deep discourse when it needs a detailed explanation. The other explains a discourse in detail whose meaning is already clear. These are two who slander the Tathāgata.”
– Two perfect examples of the first type of slander say that the words anicca and anatta are fully explained by “impermanence” and “no-self.” Those two concepts require detailed explanations.