User Exits in the Change and Transport System 
Use
You can make use of
user exits at the following times:These user exits are implemented using
Business Add-Ins. For more information, see the SAP Library under Basis Components ® ABAP Workbench ® BC - Changing the SAP Standard ®
Business Add-Ins.
Procedure
The CTS Business Add-Ins are listed in the Implementation Guide (IMG) and can be displayed with the Customizing: Execute Project transaction.