Noticed this just earlier today as well, I assume it's unintentional as it's very misleading. There's no way my factory is making 240 U-235 a minute

You can create new categories through modding, but what I think you're trying to do would require change the inventory GUI code. It's possible, there's just not any way built in already. I like the idea though, the crafting menu gets really cluttered in the late game!