Public Sub X()

    Dim rng As Range
    Dim varValue As Variant
    Dim varTemp As Variant
    Dim avarItems As Variant
    Dim intI As Integer
       
    With ActiveDocument
        Set rng = .Range( _
          Start:=.Paragraphs( 1 ).Range.Start, _
          End:=.Paragraphs(.Paragraphs.Count).Range.End)
    End With

    varValue = rng.Text
    
    avarItems = Split(varValue, Chr( 13 ))
    
    For intI = LBound(avarItems) To UBound(avarItems)
        If avarItems(intI) Like "*аааа=*" Then
            varTemp = Trim(avarItems(intI))
            avarItems(intI) = Mid(varTemp,  1 , Len(varTemp) -  1 ) _
              & "+б" & Mid(varTemp, Len(varTemp))
        End If
    Next intI
    
    varValue = Join(avarItems, Chr( 13 ))
    
    rng = varValue
End Sub

Sub X()

    Dim p As Paragraph
    Dim strTemp As String
    Dim intI As Integer
    Dim intJ As Integer
    
    For intI =  1  To ActiveDocument.Paragraphs.Count
        Set p = ActiveDocument.Paragraphs(intI)
        strTemp = p.Range.Text

        If strTemp Like "*аааа*" Then
            intJ = InStrRev(strTemp, "}")
            
            If intJ >  0  Then
                strTemp = Mid(strTemp,  1 , intJ -  1 ) & "+б" _
                  & Mid(strTemp, intJ)
            End If
            
            p.Range.Text = strTemp
        End If
    Next intI
End Sub