If the MDT database and UserExit script are still not sufficient for customizations, you can further extend MDT with the use of web services.
Jase T. Wolfe wrote a good explanation of web service in his QuickStart Guide to Using Web Services in MDT / SCCM (http://myitforum.com/myitforumwp/2013/03/07/a-quickstart-guide-to-using-web-services-in-mdt-sccm/):
"For those not completely familiar with a web service (WS), the condensed and over simplified introduction is this: A WS is a middle man that simplifies obtaining information or performing a process on behalf of the client and returning some type of data to the client. As the name suggests, the WS is a web based process which is used (in this article) by having a source client make an HTML request to the WS server, and that server returning an XML response which can be used by the client.
For instance, the build process may need to know what the correct display resolution is for the hardware it is building. The build process sends...