What is the mechanism of symptom creation produced by cellular memory? Is it always generated via nerve impulses, or can any cell type become dysfunctional and produce a noticeable or detectable physiological derangement?

As you have reasoned creatively, this can be literally any kind of discord within the cell or secondary to its influencing nerves and blood vessels with elaborated mediators of physiologic changes. It can be a dysfunction within the cells so it cannot carry out its particular functions—whether production of a hormone, taking part in signaling, or acting in concert to cause movement of the tissue as in an intestinal motility, or a muscle cell in the heart, or secretion of a substance needed for lubrication, or to produce a physiologic response downstream in other cells and tissues, or carrying out metabolic function for housekeeping purposes. Whatever is the target of negative energy from the energetic signature of discord, can be impaired potentially, and reaching the cells, can be causing an impaired function. And so there is a wide array of potential consequences that can result when trauma is not healed quickly.