Regarding the friction pull on the in breath which causes the incoming air to rub aggressively against the walls of the lungs, is that done internally through will-power action while looking inside the subtle body while doing breath infusion?

The friction pull is done using willpower as suggested in the question, but it results in a physical action where the air rubs and you can hear it doing so. This verifies that it is not imaginary and it is not a willpower action which is ignored by the body.

To test about this, sit still for a moment. Then observe the normal breath pattern for six in/out breaths. These breaths will be silent almost because they are done involuntarily by the automatic system of breathing in the body.

Then with eyes closed and being attentive, slowly and steadily pull in a breath. Then allow the system to exhale on its own. Then with eyes closed and being attentive again, slowly and steadily pull in another breath, except this time pull with more force. You should notice that in the nostrils the air rubs against the inner nostrils/sinus surface. You should keep the eyes closed and focus. Then you may notice this be feeling the air as well as by hearing the rubbing action inside your head.

This same type of action will happen inside the lungs if one practices for a time and is attentive.

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Some of the muscles and cells in the body do not act in a way to facilitate kundalini yoga breath infusion. However if one practices for a time, these attitudes of the cells and muscles may change. For instance recently on reviewing a student’s practice, I brought it to his attention that he was chest cavity breathing. This was because while doing kapalabhati/bhastrika, his chest cavity was raising up and then dropping noticeably. But that is not the way for that breath. I encouraged him to relax that part of the body and allow lower abdomen movement in and out instead. He could not do this on the spur of the moment but in time, if he practices, this will happen.

It indicates that beginners have an in and out motion in the upper part of the lungs. This should change to where the air goes down through the lungs and hits the bottoms. Merely making a willpower command may not cause this to happen initially, even though in the long term, it may happen.