Some courses, such as 199 & 195, are designed to be taken more than once since the content of the course varies. The UCI General Catalogue listing for the course indicates if it's approved for repetition and how often it may be repeated for credit.
All other courses may only be repeated when the student earns an 'NP' (no pass) or a grade of 'C-' or below. Any repeat of a course with a C or higher grade will be coded as an unauthorized repeat and no credit or grade will be posted.