What do you want to redesign, exactly? Your question is vague.
So my answer will be equally vague: Do you have a gunsmith license? Do you have the right to modify, rebuild or create from parts Prohibited items?
Do you have the right to buy and sell Prohibited items?
If you answer no to any of the above and the product you want to work with is an airsoft gun instead of an accessory, you are out of luck.