The following VBA example builds crop marks around selected objects and sets their outline color to the registration color.
Sub Test()
Const Offset As Double = 1 ' Crop mark offset
Const Length As Double = 5 ' Crop mark length
Dim s As Shape
Dim r As New ShapeRange
Dim lyr As Layer
Dim x1 As Double, y1 As Double, x2 As Double, y2 As Double
Set s = ActiveSelection
Set lyr = ActiveDocument.ActiveLayer
ActiveDocument.Unit = cdrMillimeter
ActiveDocument.ReferencePoint = cdrTopLeft
x1 = s.PositionX
y1 = s.PositionY
ActiveDocument.ReferencePoint = cdrBottomRight
x2 = s.PositionX
y2 = s.PositionY
r.Add lyr.CreateLineSegment(x1 - Length - Offset, y1, x1 - Offset, y1)
r.Add lyr.CreateLineSegment(x1, y1 + Length + Offset, x1, y1 + Offset)
r.Add lyr.CreateLineSegment(x2 + Offset, y1, x2 + Length + Offset, y1)
r.Add lyr.CreateLineSegment(x2, y1 + Length + Offset, x2, y1 + Offset)
r.Add lyr.CreateLineSegment(x1 - Length - Offset, y2, x1 - Offset, y2)
r.Add lyr.CreateLineSegment(x1, y2 - Length - Offset, x1, y2 - Offset)
r.Add lyr.CreateLineSegment(x2 + Offset, y2, x2 + Length + Offset, y2)
r.Add lyr.CreateLineSegment(x2, y2 - Length - Offset, x2, y2 - Offset)
For Each s In r
s.Outline.Width = 0.1
s.Outline.Color.RegistrationAssign
Next s
End Sub