Sure! Admins and users with managerial permissions on a curriculum are able to set any curriculum course as optional, meaning that its completion won't be needed for the curriculum completion.
Simply select Training > Curricula from the upper navigation bar and then click on the Manage Curriculum field of your Curriculum.
Click on Edit Courses under Courses and select which courses are needed for curriculum completion:
If a course is marked to not be needed for curriculum completion, then a note will also appear for the user under this course's name, informing them that the course is not needed for curriculum completion.