You can edit the fiber link for a point-to-point CTC connection. Open the CTC Connections dialog by choosing CTC Connections... from the Edit menu. Choose the point-to-point connection and press the Fiber Link... button to open the Edit Fiber Link dialog. You can then edit the composition of the Fiber link between the CHPIDs. For more details, see Editing fiber links.
Note that CTC connections through switches have two fiber links, one on each switch port. To edit those fiber links, open the Switch dialog by double-clicking on the switch in the configuration diagram. Select the desired switch port and click on the Fiber Link... button to display the Edit Fiber Link dialog.