Hi,
PlayMaker only works with the runtime library, the "UnityEditor" namespace is only available within Unity Editor, this is used to run all the various views and editor, but can not be used by the game itself.
you can not change the target Resolution after you published. The solution is to create dynamic layout, and if you are looking for supporting Retina, then you'll have to provide both set of graphics. I never did this yet, so correct me if I am wrong here.
Right now, I would simply get the resolution of the screen using "Get screen height" and "Get Screen Width" Actions:
https://hutonggames.fogbugz.com/default.asp?W446Bye,
Jean