This is easy to automate so long as all the site specific customizations are implemented within the VMD using configurations and python scripting. For each site the sample data (i.e. HL7 messages) can be stored and then run through the VMD file using the msgtransform tool to validate the behavior - i.e. standard input and expected output.

This can be automated with scripting. A batch file can be used to perform automated regression tests that will allow you to compare changes in output rapidly.