Sub Demo()
Application.ScreenUpdating = False
With ActiveDocument.Range
  With .Find
    .ClearFormatting
    .Replacement.ClearFormatting
    .Text = "%"
    .Replacement.Text = ""
    .Forward = True
    .Wrap = wdFindStop
    .Format = False
    .MatchCase = False
    .MatchWholeWord = False
    .MatchWildcards = False
    .MatchSoundsLike = False
    .MatchAllWordForms = False
    .Execute
  End With
  Do While .Find.Found
    If .Information(wdWithInTable) = True Then
      If .Cells(1).Shading.BackgroundPatternColorIndex = wdGray50 Then .Text = "CB1"
    End If
    If .End = ActiveDocument.Range.End Then Exit Sub
    .Collapse wdCollapseEnd
    .Find.Execute
  Loop
End With
Application.ScreenUpdating = True
End Sub