It looks so obvious that Curve (Line and Arc) should be modifiable through the Revit API, and so do those elements that are based on it such as Grid. However, it's verified not true through many trials and errors.
The fact is clear as such.
The Curve has an end point retrieving method, GetEndPoint(int index), but not a setting one.
The Grid.Curve is read-only thus it is not possible through creating a new Curve and resetting it to the Grid to change the Grid geometry.
By the way, the Grid.SetCurveInView(...) does not work either, as it requires a coincident curve as the original one!
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