Milarepa and Avalokiteshvara practice In the Vajrayana tradition, where did Milarepa state that it was possible to use the practice of Chenrézik (Avalokiteshvara) instead of the one of Hevajra?
There is a qualitative difference between a practice which uses Avalokitasvara (Chenrezig) for visualizations, etc., and the practice that was used by Avalokitasvara to reach enlightenment. They are not the same.
The Mahayana/Vajrayna Surangama Sutra is of immeasurable value in this regard. It describes this path, which was taken by Buddha and Manjusri, as well as Avalokitasvara, and all Buddhas. See Manjushri’s Summation from the Surangama Sutra: https://bit.ly/ManjushriSummation
Jamyang Khyentse Chökyi Lodrö’s “The Light That Makes Things Clear: A Prophecy of Things to Come,” (“ma 'ongs lung bstan gsal byed sgron me zhes bya ba bzhugs so”) indicates this meditation method is the one most useful for beings such as we, in the Dharma ending time. See: http://bit.ly/TheLightThatMakesThingsClear
Using this method with the support of inner spontaneous sounds* results in the accomplishment of Great Responsiveness (Mahakaruna) and the supreme siddhi.
There is a universal understanding of this path. See: http://bit.ly/PathToEnlightenment
The Tibetan Nyingma teacher, Khenpo Sodargye Rinpoche, is teaching the Surangama Sutra at the Larung Gar center, in Sêrtar County of Garzê Tibetan Autonomous Prefecture, in Sichuan, China, also known as Kham, which he is the head of, since late 2019.
The english translations of those teachings are on Youtube. This is the webpage announcing his teachings: http://khenposodargye.org/teachings/khenpos-classical-teachings/surangama-sutra/
Note: many traditions use inner spontaneous sounds to different purposes and with different interpretations. Here are a list of keywords to search with: Abstract Sound, Astral Sound, Anāhata Nāda, Dharma Sound of the Diamond Samadhi, Chönyid kyi rangdra (Chos Nyid Kyi Rang Sgra), Dharmata Swayambhu Nada, Divine Tremoring, Eternal Sound, Holy Stream of Sound, Inner sacred sound, Inner Sound, Music of the Spheres, Nada-Brahman, Omkara Dhvarni, Primordial Sound, Resonance of Emptiness, Sawt-e-sarmad, Sacred Sound, Shabda, Shabda Brahman, Sound of Creation, Sound of Silence, Soundless Sound, Thunder of Silence, Transcendental Sound, Unborn Sound, Unstruck Sound, Word of God.