Customize Market Basket Upload with Sub-Total Command

I’m working on a project to partially automate a current manual process. We will use the Market Basket Upload template to import order information into our Eclipse system. We would like to add a command / code to the file to insert comment lines and sub-totals throughout the form. Does anyone know how we could do this and what those command lines would be and where we could place them on the market basket upload template? Thanks for any support!