One of my favorite reasons for using MDT is that it builds images for you. If you maintain a separate share just for builds, you can be 100% certain the image you build today will be the same as the one you build tomorrow, only difference is how updated it is.
The real trick of this whole process however is how to get the task sequence to pause so that you can do what it is that you need to do inside your reference build, and then resume the task sequence so that can capture it.
Right click the build task sequence and select properties. Then select Add and then choose run command line.
Use the super handy LTISuspend.wsf script that comes with MDT.
Running the LTI Suspend script pauses a task sequence, and places a resume shortcut on your desktop. This trick also comes in handy when you’re testing application deployments in a VM. This lets you pause the task sequence, make a snapshot in your VM, and then tweak the applications. If you’re not happy with the way an application is deploying, you can test and retest very quickly instead of having to start the deployment all over again from scratch on a physical computer.