Dear Paul,
Yes, I realized it is expensive, won't buy the same thing again.
But I still consider it is an official alteration after thinking it again. First, the SN area was carefully polished and the style of engraved serial number looks similar to my Order of red star which awarded in late 1943, I don't think an ordinary people can do this. Second, there are similar examples in N. Strekalov and V. Durov's Red Banner book on page 113, the book also mentioned the purpose is exchanging the old type Red Banner (read it with Google translation ). Third, patina of polished alteration area match other area, means the alteration has been done long time ago, probably the same period the Red Banner was produced.
Best wishes,
Spartan