To add additional clauses, you can use the “insert clause” change, and subject that change to certain conditions that will be triggered when a certain answer to some question is fulfilled. The reason why this works slightly different than simply swapping alternatives, is that there are so much more possibilities that can apply, hence the reason to have more flexibility.
For example, you could ask a question “Which of the following optional clauses should be inserted?”, and add predefined elements “alpha” and “beta”.
If the user should be allowed to simultaneously insert both alpha & beta (which I assume you want), then you have to set that question’s options to “multiple answers”. Also, disallow free answers by checking the box.
Next, you need to insert an “insert clause” change and choose the relevant location in your contract (below/above/subclause of some other clause), and subject that change to a condition that is triggered when option “alpha” is selected by the user.
The same needs to be done for option “beta”, or whatever other clauses you would like to add.