I have an app that obtains all of it's configuration information from Voice Portal / Experience Portal variables. However, I would like to be able to test the system via web (by manually going to http://<host>/Application/Start).

However, the VP vars are all set to their default values. I remember from 4.x that if you wanted a var called x to have the value 1, you could do it by going to http://<host>/Application/Start?x=1

However, this is not working for me right now. I change the value on the URL parameter, but it does not get changed. How can I change it, so that I can test before connecting my app to VP?

Configurable application variables (CAV) are not supported in the web simulation but are in the regular simulation.

If you run the application in simulation and then in the simulation profile you set the value of the CAv you can test that way.

And how does the simulation profile set the VP Variables with the values in the simulation profile?
Could I simulate that outside Eclipse?

NO you need to simulate with in eclipse using the built-in simulation.

In window->Preferences

Select Avaya Aura-> Application Simulation -> Simulation Profiles

Then edit your profile.

Select Varaible Administration and then import the CAV from your application and then alter the values and run in the simulation.