Измените .Wrap = wdFindContinue на .Wrap = wdFindStop в вашем макросе:
' Macro1 Macro ' ' Selection.Find.ClearFormatting Selection.Find.Replacement.ClearFormatting With Selection.Find .Text = "ä" .Replacement.Text = ChrW(257) .Forward = True .Wrap = wdFindContinue