Yes, you can assign only Guided Reading Mode questions to students when assigning a Library Lesson.
Guided Reading Mode is automatically enabled for Library Lessons. Ensure the Guided Reading Mode toggle is set to YES and click the "Assign Assessment Questions" to toggle it to NO.
You can enable or disable Guided Reading Mode on existing assignments by clicking pencil icon in the top-right corner of your assignment on your Assignments page to edit the assignment. Please note, you cannot edit the Assessment Questions.
Assignments with only Guided Reading Mode will always have annotations, read aloud, and translate enabled. These features cannot be disabled at this time.
For more information on how to customize a Library Lesson, please see the FAQ: Can I customize which questions my students answer on Library Lessons?