The publishing tool’s class that provides some customizations to the appearance and behavior of the Publish window must implement ISPCLPublishDialogCustom, which is defined in SPCLPublishCustomInterface.dll.
The implementation class must inherit SPCLPublishCustomInterfaceSerialization.
Following code is a VB.NET example of the beginning of an implementation class for ISPCLPublishDialogCustom:
Class SPCLTestToolPublishDialogCustom
Inherits SPCLPublishCustomInterfaceSerialization
Implements ISPCLPublishDialogCustom