Yep, and what should happen is that when you enter a ruleset that uses a %{VARIABLE}, a text field should appear to let you specify the value to use for testing

Yep, and what should happen is that when you enter a ruleset that uses a %{VARIABLE}, a text field should appear to let you specify the value to use for testing. If this does not happen for you, would you mind using the problem report button on the site? It will let me see your ruleset and a debug log to troubleshoot.