While Paul is correct with regard to sentences, and such a task might even be impossible with access to the complete document. However I find that in these forums some people write 'sentence' when they are referring to sentences that form a paragraph. If the text is a complete paragraph, the following macro will format that paragraph if the cursor is placed in it before running it:
Sub Macro1()
Dim oRng As Range, oEnd As Range
Set oRng = Selection.Paragraphs(1).Range
Set oEnd = oRng.Duplicate
oEnd.End = oEnd.End - 1
oEnd.MoveEndWhile ".", wdBackward
oEnd.Collapse 0
oRng.Collapse 1
oRng.MoveEndUntil "-"
oRng.End = oRng.End + 2
If Len(oRng.Text) < 11 Then
oEnd.Text = Replace(oRng.Text, " - ", "")
oEnd.InsertBefore " ("
oEnd.InsertAfter ")"
oRng.Text = ""
End If
Set oRng = Nothing
Set oEnd = Nothing
End Sub