Currently I am studying the traditional version of integrated Chinese second edition. Once I am done I would like to add the simplified variants of the words in the list. How do I go about this?

Hello. I think you would go to Account, then Study settings & change the Character style box to 'both'.
Hope this helps your Question :)

I figured I would have to do that, but would that automatically add the simplified version for the traditional words I already have?

You would then go to the "study settings" on that list's page and set yourself back to the beginning of the list. The missing traditional forms will then be gradually added in as you progress again through the list.