This dialog is shown when you are about to change the control code of the control.
You have two options:
This option will assign the new code to the control, AND at the same time substitute the "old" control code with the new one across all courses that use this control.
This option is useful when you want to entirely change the control code of a control, and still keep the same courses visiting this control.
This option will assign the new code to the control. But it will NOT change any occurrences of the "old" control code in the courses.
This option is useful when you want to "swap" two controls without changing the courses.
However, use this option carefully:
When using this option, there may still be courses that visit a control with the "old" control code. Since you rename the control, such a control will no longer exist. You should make sure to create a new control with the "old" control code (or rename another control) in order to keep the course database consistent.