If there is ever a need to adjust the employee contributions on a savings plan (403(b), 457, Roth), it is best to do so on the actual enrollment.  A manual 403 event can be used to make this adjustment.  While the system will allow for the adjustment on a pay line during payroll, the change made on a pay line may not be reflected in the subsequent vendor remittance.  If a change must happen on a pay line, also make the corresponding change in the enrollment.