You can access the Flash Stage from your C#/JS scripts in the following way:
ActionScript.Import("com.unity.UnityNative");
ActionScript.Statement("trace(UnityNative.stage);");
As an example, the following C# code will output the flashvars supplied to a SWF:
ActionScript.Import("com.unity.UnityNative");
ActionScript.Statement(
"var params:Object = LoaderInfo(UnityNative.stage.loaderInfo).parameters;" +
"var key:String;" +
"for (key in params) {" +
"trace(key + '=' + params[key]);" +
"}"
);