Mantras are only endowed with transformative power if given in initiation (dīkṣa) with the mouth of a Expert. It's not so much suitable pronunciation, but relatively the facility with which the mantra is endowed that gives it reworking capability. Most on the web reference entries and articles or blog posts https://griffinvjyjw.blogsidea.com/43351035/mantra-things-to-know-before-you-buy