Yes, you can add/delete a course in the Structure tab of a Learning Path/Certification, provided there are no active enrollments for that Learning Path/Certification. Adding or deleting courses after learners have already enrolled may disrupt their learning experience. Therefore, it is recommended to make any changes to the Learning Path/Certification before learners start enrolling in it. Once there are active enrollments, the option to add or delete courses will be disabled to maintain the integrity of the learning path for the enrolled learners.