Generate new invoice triggered by particular sales item

Hello,

I am new to Netsuite (Small Business edition) and have some pretty fundamental questions regarding scripting and customisation. My account is an admin account.

I am setting up Netsuite to run my solar sales business. When I create invoices to my customers they often include rebates. If I add one of these rebates (discount) to a customer invoice I want to automatically generate an invoice to the government to be compensated for the rebate.

The value of the invoice to the government should be a direct reflection of the original discount or based on a global variable set somewhere (but easily updated).