I’ve used Category icons component to change the category locks icon to
unlock-alt, which is great.
They are applied to all categories and subcategories appropriately except the
category-box-heading. You’ll note that the subcategory titles have the replacement icon with no problem:
When inspecting the boxes, I note that the text for the category-box-heading is not wrapped in `category name here, and the icon assigned to it is the default one (not the one it has been changed to).
Apologies if this is actually related to the Theme Component, but I’m pretty sure it is something in core.