I don't think it is possible to do as an edit. I think you would have to collect as much data as possible about the existing detail views and their 'fences', then recreate the detail views.
The "CircularFence" Boolean property of a "DetailDrawingView object is a 'Read Only' property.
And the FenceCornerOne & FenceCornerTwo properties (Point2D objects) can't be set if the CircularFence property is True.
Here's some quickie code that shows you what data is available and readable/writable for the DetailDrawingVeiw.
Dim oView As DetailDrawingView = ThisDrawing.Document.ActiveSheet.DrawingViews.Item(1)
'AttachPoint can be Nothing and can be set to Nothing later
Dim oAttachPoint As GeometryIntent = oView.AttachPoint
'oCenter can't be set, if it is already attached to something (oAttachPoint returns an object)
Dim oCenter As Point2d = oView.FenceCenter
'Get & Set
Dim oBLayer As Layer = oView.BoundaryLayer
'Read Only property
Dim oCircular As Boolean = oView.CircularFence
Dim oRadius As Double
If oCircular = True Then
oRadius = oView.FenceRadius
Else
'oC1 will be Nothing and can't be set if oCircular = True
Dim oC1 As Point2d = oView.FenceCornerOne
Dim oC2 As Point2d = oView.FenceCornerTwo
End If
'Get or Set
Dim oSmooth As Boolean = oView.IsBreakLineSmooth
Wesley Crihfield

(Not an Autodesk Employee)