Ok, from how the antiquarian works.
her hero.info file has a call for the ID: extra_stack_limit: .id antiquarian_gold
This ID (as you pointed out) is called from the base.inventory.extra_stack_limits. For now I would just edit that file instead of making it’s own. Try the following code in it.
extra_stack_limit: .id torch_stack .item_type supply .item_id "torch" .amount 4