Currently, the GridSplitter Element provides the option to set a Custom Style for its 'Preview' Part, which shows the GridSplitter in a 'ghosted' presentation during the click-and-drag process of using the GridSplitter at runtime.

It appears however, that creating a new Style for this 'Preview' part is not supported, and all changes within the Style's Properties generate XAML errors.

See attached video.

Repro Steps:

1) Create a Studio Project containing a MainPage.xaml
2) Introduce a GridSplitter Element to the Root Grid of the Page, and give it a size of 256x256 to make it nice and visible.
3) From the Navigator, right-click on the GridSplitter Element, and from its Context Menu, navigate to Styles --> Preview --> Create
This will create a Style in the Inline Style Dummy Editor.

4) Within the Style, pick any Property from the Style's Properties Panel (Opacity is a good choice)

5) Adjust the value of the chosen Property.

Observe how the change in Style Property Value instantly causes a XAML error in studio.
Observe how if Opacity was chosen as the Property, the newly-chosen value not logging, and 'snapping' back to its original value.

Expected Results: Properties within an accessible Style in Studio can be freely modified and saved without generating XAML errors.