No we don't provide any command line mechanism for overriding the DefaultApplicationPath setting contained in the test list settings.
However one of my QA testers suggested that you implement a Execution Extension
. In there you can write your own code to set the DefaultApplicationPath before the test starts. You can set it using code like this:
public void OnBeforeTestStarted(ExecutionContext executionContext, ArtOfTest.WebAii.Design.ProjectModel.Test test)
test.WpfAppPath = @"c:\myfolder\myapp.exe";
You can extend this to implement code that would read the value from a config file and then set the property from that config file.