The following VBA example creates cropmarks around one or more selected objects and assigns registration color to each of them.
Sub Test()
Const Offset As Double = 1 ' Cropmark offset
Const Length As Double = 5 ' Cropmark length
Dim x As Double, y As Double, w As Double, h As Double
Dim c As Color
ActiveDocument.Unit = cdrMillimeter
Set c = CreateRegistrationColor()
ActiveSelection.GetBoundingBox x, y, w, h, True
ActiveLayer.CreateLineSegment(x - Length - Offset, y, x - Offset, y).Outline.Color = c
ActiveLayer.CreateLineSegment(x, y - Length - Offset, x, y - Offset).Outline.Color = c
ActiveLayer.CreateLineSegment(x + w + Offset, y, x + w + Length + Offset, y).Outline.Color = c
ActiveLayer.CreateLineSegment(x + w, y - Length - Offset, x + w, y - Offset).Outline.Color = c
ActiveLayer.CreateLineSegment(x - Length - Offset, y + h, x - Offset, y + h).Outline.Color = c
ActiveLayer.CreateLineSegment(x, y + h + Length + Offset, x, y + h + Offset).Outline.Color = c
ActiveLayer.CreateLineSegment(x + w + Offset, y + h, x + w + Length + Offset, y + h).Outline.Color = c
ActiveLayer.CreateLineSegment(x + w, y + h + Length + Offset, x + w, y + h + Offset).Outline.Color = c
End Sub