HSN Code Required in India Market

Hello,
As per new regulation in indian market, regulator mandate HSN code for every product category, how can i put my product HSN code at the time of product listing or add custom field.

Hi,
Is it a code per product or per category.
If per product and it isnt used for claculations - why not use one of the product fields like MPN, EAN etc that you dont use now. To display one of these on the product/category screens then do a search on the forums, or get an extension