When I mention "Overriding" in reference to a StackScript, this is what I mean.

The supplied StackScript has default values set for it. These defaults are set to make the demo application as simple to deploy as possible. When you want to deploy a different demo to the "default demo" you will certainly have to override some settings that have been supplied as default values in your StackScript.

So, taking "Demo 1" here I can see that "Demo 1" invites us to override the following settings.

 set "The Display name for your website e.g. My Demo Website" to "My Joomla Demo"  
 set "BASELINE DB REPOSITORY" to "joomlademo-db-baseline" 
 set "APPLICATION BASELINE SOURCECODE REPOSITORY" to "joomlademo-webroot-sourcecode-baseline"

Before I apply the invited overrides in order to build "Demo 1", the original StackScript (with its default values set) looks like this:

And then once I have applied the overrides suggested/required, it looks like this:

And so the change in values that you see is what it means to override the the values of the supplied StackScript