Sub blah()
Do While ActiveCell <> ""
If ActiveCell = "TRNS" Then
Selection.EntireRow.Insert Shift:=xlDown
Selection.EntireRow.Insert Shift:=xlDown
ActiveCell = "ENDTRNS"
ActiveCell.Offset(2, 0).Select
End If
ActiveCell.Offset(1, 0).Select
Loop
End Sub

First select the top of column  A where you want this to start from (It
might be a good idea to start one cell down from the first "TRNS")
then run the macro