Unfortunately (other than assigning a default ENTER and ESC action) keybindings are not something we can mod.
However, I'm pretty sure the crafting window skillbar uses whatever hotkeys you have assigned for Hotbar 1, so you should be able to map additional numpad keys to hotbar 1 keys 1-6 and achieve the effect you're after.
You will very likely run into several binding conflicts and need to reassign stuff already assigned to the numpad.
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