Yep! You can apply the premade transforms to backgrounds, characters, or entire layers.
I have an update that will include an example of this, but in the mean time you can set the Mesh property to true on a layer(or a transform you make/edit) and apply it to an entire layer, which can include anything on the screen that you add to it.
The master layer is the one you'd want to apply a transform to most of the time, if you're doing screen wide shaders.