Direct user flow to exclusively mutual forms

I have a form where a user is presented with two options. They can either select (via a checkbox grid) flags for products, and exclude some specific items from that list, OR, specify only the items they want to include (regardless of the state of flags). I'd like to present this to the user in an intuitive way. This is for a web application.

What options could I use for this? There are other parts of the form that are hidden within an accordion (but are required, which makes me think it shouldn't be in an accordion), and an accordion within an accordion doesn't feel right. I could take the other controls out of the accordion, and hide these within their own accordion, but then the rest of the form gets really long.

The idea of a tabbed pane came to mind, but it seems a bit overkill for two tabs.