I can’t find a GetRenderTransformPropertyName function, or anything similar, on UWidget so that solution doesn’t work in this case. I see no other solution than hard-coding it:
if (PropertyName == FName("RenderTransform"))
and checking from time time time, preferably with a unit test, that the if-block is executed when you expect it to. If the property is ever renamed then there is nothing the compiler can do to help you with a hard-coded property name like this.