"it is possible to extend the applications through custom DSC development."
It's definitely possible to create your own custom service. The DSC is just a jar file that contains a bunch of classes and an application.xml file that defines some metadata.
You wouldn't be able to modify the Foundation services, because we don't provide the source for them.
You can find information on creating custom DSC at
http://www.adobe.com/devnet/livecycle/articles/extend_forms.htmlThis is still basic. We are working on a more advanced one which should be posted in the next few weeks.
Jasmin