CommonLit only allows you to create an assignment for a given text once in each class. Therefore, you cannot assign a text with only the multiple-choice Assessment Questions and then create another assignment for the same text with only short-answer Assessment Questions for the same class.
Please note, it is not currently possible to edit the Assessment Options for a Library Lesson after it has been created.
However, if you created an assignment and selected the wrong Assessment Options, you can delete the assignment by clicking the trash can icon for that assignment on your Assignments page and then recreate it with the correct Assessment Questions. If you already have student data and do not want to delete the assignment, you can choose to create a second version of the assignment with different Assessment Options from by creating an Individual or Small Group assignment. However, data for these assignments will not be included in Student Performance or Class Performance data.