How can I modify modal property in window from code?

Hi.
I want to extend blutility scripted actions. I want to modify modal dialog’s property in code.
I realize, if I want to modify slate property value. I should use property handle.
But property handle is created from slate’s builder like IDetailLayoutBuilder
Inherited class from Menu, ToolBar, DetailPanel is support CustomizeDetails function that give Builder parameter.
But I can’t find way to use builder for window modal slate.
How can I get property handler in window slate? or Is there other way?

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296911-dialog.png