AdRotator can do this yes, just the trick of doing it through the integration.
You can try this for now:
var manager = GameObject.Find("AdRotatorManagement");
var AdRotator = manager.GetComponent<AdRotatorUnitySDK.Assets.Plugins.AdRotatorManagement>();
AdRotator.AdSettings.IsEnabled = false;
Which should achieve what you are trying to do, note it will cause an error in the editor currently because it expects the platform project to be running.
Let me know if this works for you. Worked fine in testing.
As for the AdSizes, this is a common problem with so many ad providers and we are looking at solutions, it comes down to how ad providers react to different ad size settings, some will get the closest match if the pixel rations are not exact, others will just
deliver a default ad size. Just experiment with which ever ad size fits you.
In the future we intend to abstract the ad size configuration so you always get the closest match but it's a fair amount of work to implement.