Whilst I agree with Andrew regarding the desirability of avoiding double rows, I think a macro can also be made to replicate the structure fairly reliably where such avoidance isn't practical. For example:
Code:
Sub Demo()
Application.ScreenUpdating = False
Dim RngSrc As Range, RngTgt As Range
With Selection
If .Information(wdWithInTable) = False Then Exit Sub
With .Tables(1)
Set RngSrc = .Rows(.Rows.Count - 1).Range
RngSrc.End = .Range.End
Set RngTgt = .Range
RngTgt.Collapse wdCollapseEnd
RngTgt.FormattedText = RngSrc.FormattedText
.Rows(.Rows.Count - 1).Range.Delete
.Rows(.Rows.Count - 1).Cells(1).Range.Text = (.Rows.Count - 1) / 2
End With
End With
Application.ScreenUpdating = True
End Sub