So I was noodling the weird science implications of the abhumans and may have something: a herbivorous cecum.
So I presume many of the abhumans have chosen a herbivore as their “sprit animal.” You wouldn’t be emulating a cow, horse, or elephant very well if you didn’t primarily subsist on leafy greens, which while edible to humans don’t offer much sustenance. I expect the solution would be to change their anatomy to include a herbivorous cecum so they can digest cellulose.
So what I would propose here is that the MC learns about self-change from the abhumans and this particular change is of specific interest as a consequence of their experience during the starving winter in G1. The implication isn’t a total solution of the famine, but it might allow some caloric replacement from easily edible cellulose like flowers, fruit skin and husks, leafy greens, and tubers. Basically those foods that are really only a source of fiber for an unmodified human. This would also allow self-taught theurges to escape settlements and survive more readily in the wilderness. Obvious downside is crossing wards.
This might be a viable option for the inner voice/mass sacrificial theurgy path. It’s anatomy we already have, it would be reasonable for the process to be learned by and sought by the MC, and it has strategic utility later in the story.