Yidam is Ostensibly the term attributed to a Tantric Deity upon whom one focuses with the objective of evolving oneself to that of enlightenment.
With today's understanding of mind matter interface, Buddhism's Vajrayana path was ahead of the curve. Though the deeper subtitles are pretty lost on people who use modern manifestation techniques to acquire egoistic wants, a sincere desire to attain the highest version of one's self during our time upon our mother earth is the perfect starting point. Bringing the heart filled full-bodied feelings of future attainment into the present moment is what both of these 'technique' have in common. We know that nothing intrinsically exists thanks to quantum physics, again something that the wisdom teachers of old knew all about, and this is the fundamental truth that underlies mundane reality. Now, I would not dare to know or assume for sure whether those enlightened beings also knew about the 96% of the unknown non material universe and if they had access to it. Whether or not it is within these realms that higher beings, deities, Gods and Goddesses or fairies and earth bound spirits and the likes reside as actual entities of sorts who can materialize either into an avatar on earth or as 'spirit guides' to those who call upon them. Or if our meditational communes with them rest purely as a projection of our mind rendering Yidams and deities purely psychological. To determine what is actual knowledge from the Buddhist masters is difficult as many describe them as either or both, though I do feel that much of their teachings are gauged and geared for the modern Western mentality and appropriate for our era. The wisdom masters were correct over a great many things a very long time ago and it is only now that Western man is quantifying much of it, so who knows if ascended masters, Deities and Dakinis and so forth really are inherently existing beyond our 4% universe with access to us through the veil that appears to divide us, playing their part as we are, in a vastly, unimaginably big unfurling picture where time and space are purely relative, if we're all part of some great evolving one-ness or if it's all void and it's all in our head.
It is my contention that much of what we call paranormal or magic is in relation with the unknown universe and that our meditations and body work (chakra balancing to pineal gland activation, etc) is 'fine-tuning our atoms' for clearer reception. There are ultimately no contradictions in wisdom teachings, only humans' dogmatic approach to ego and sectarianism that is the convoluted result of the subtleties of 'audience appropriate' teachings. To understand that every'thing' is wave energy potential until it becomes conscious particle, that we are mind in transient meat-sacks that form patterns in our brain-matter based upon our sentient experiences that imprint the subtle mind, often carried over into the next meat-sack (though time is not linear so the "next" could be at any time and subtle mind is not necessarily attached in a singular way as we would recognize it) so to work upon healthily negating these construed emotional obstacles through understanding them and transmuting them, recalling our more than-mundane-ness through relationship with the most sublime personification coherent with our personality at the time that, in one sense gives as the 'strength' to heal these "kleshas". Though this is a very simplified nutshell of a paragraph, and what and where the consciousness source resides to form particle from wave in the beginning, if there even is such a thing as "beginning", is in part what has kept many a theologian and scientist busy for a life time let alone as the tragic 'excuse' for religious conquest and cruelty.
The Yidam is not an archetype. An archetype is essentially a psychological attribute being expressed. The Greeks were masters at explaining the complexities of life and emotional relations through their use of God and Goddess archetypes and their various shenanigans. Understanding the archetype/s that we are expressing or less commonly, wish to aspire to, can better explain our inner processing and inter-personal experiences. The Yidam however, is beyond our world and more likely experienced as a personification of a 'super-super-consciousness' that may or may not exist somewhere beyond the veil, in an alternative reality, in that 96% beyond our mere observable 4% and we tap into that ultra-cosmic mind-stream through visualizations and mindfulness. We 'hook' ourselves to it firstly through seeing it in our mind's eye, often with a visual aid, and then, in highest yoga, actually start to embody it. It could also be described as the perfection of (as Jung coined) a 'collective conscious' concept that we ascribe to with a desire to attain, to realise, in our own human form. This is a rudimentary explanation but gives you an idea.
His Holiness the Dalai Lama noted the following in the book 'The Heart Sutra':
"It is very important to understand that the core teachings of the Theravada tradition embodied in the Pali scriptures are the foundation of the Buddha's teachings. Beginning with these teachings, one can then draw on the insights contained in the detailed explanations of the Sanskrit Mahayana tradition. Finally, integrating techniques and perspectives from the Vajrayana texts can further enhance one's understanding. But without a foundation in the core teachings embodied in the Pali tradition, simply proclaiming oneself a follower of the Mahayana is meaningless.
If one has this kind of deeper understanding of various scriptures and their interpretation, one is spared from harboring mis-taken notions of conflicts between the "Greater" versus the "Lesser" Vehicle (Hinayana). Sometimes there is a regrettable tendency on the part of certain followers of the Mahayana to disparage the teachings of the Theravada, claiming that they are the teachings of the Lesser Vehicle, and thereby not suited to one's own personal practice. Similarly, on the part of followers of the Pali tradition, there is sometimes a tendency to reject the validity of the Mahayana teachings, claiming they are not actually the Buddha's teachings.
As we move into our examination of the Heart Sutra, what is important is to understand deeply how these traditions complement each other and to see how, at the individual level, each of us can integrate all these core teachings into our personal practice."
There have been a few decades now of hard research and documentation on the effects of meditation as well as other super-natural phenomenon. Neurology and how the brain rewires through particular practices has become common knowledge. (More here) So it stands to perfect reason, that negative patterns become unconscious habits and likewise, positive patterns positive habits. There is also the language of symbols and colour, something that Carl Jung spent much of his life researching, and its effects on the conscious, unconscious as well as physical brain. Again, the ancients knew much about this and whilst it is fair to say that social, political and cultural fashions of the time influenced certain aspects of the art work, the sacred art was fundamental imagery. Visual information in a form the intuitive mind could understand, bypassing the analytical and linear part of the brain. Meaning that, aside from reading not being necessary, the stubborn ego would be less likely to put up a fight to remain in its safety patterns of familiarity, therefore allowing a neurological restructuring.
Focusing upon a Yidam, will indeed rewire one's brain, your emotional patterns and evolve your soul.