Copy and paste the row into a new sheet with changes in cell value (month) based on a different cell value

here's a solution based on the problem described

Sub test()
Dim Dic As Object: Set Dic = CreateObject("Scripting.Dictionary")
Dim x&, cnt&, cl As Range, SDt$, EDt$, Dif As Date, Key As Variant
With Sheets("Source")
    x = .Cells(Rows.Count, "A").End(xlUp).Row
    For Each cl In .Range(.[A2], .Cells(x, "A"))
        cnt = 1
        Dic.Add cnt & ";" & cl.Text & ";" & cl.Offset(, 2).Text & ";" & cl.Offset(, 3).Text, Nothing
        Dif = DateAdd("m", cl.Offset(, 1).Value, cl.Offset(, 3).Value)
        While Year(Dif) = 2015
            cnt = cnt + 1
            SDt = Right("0" & Month(Dif), 2) & "-" & Right("0" & Day(cl.Offset(, 2).Value), 2) & "-" & Year(Dif)
            EDt = Right("0" & Month(Dif), 2) & "-" & Right("0" & Day(cl.Offset(, 3).Value), 2) & "-" & Year(Dif)
            Dic.Add cnt & ";" & cl.Text & ";" & SDt & ";" & EDt, Nothing
            Dif = DateAdd("m", cl.Offset(, 1).Value, Dif)
        Wend
    Next cl
End With
Sheets("Output").Activate: x = 2 ''
With Sheets("Output")
    For Each Key In Dic
       .Range(.Cells(x, 1), Cells(x, 4)) = Split(Key, ";")
        x = x + 1
    Next Key
    .[C1:D1].Value = Sheets("Source").[C1:D1].Value
    .[B1] = Sheets("Source").[A1]
    .[A1] = "TASK ITERATION"
End With
End Sub

      

        
        
        
      

    

Start sheet

Output sheet