You are stuck with it as is. You cannot change the barrel, ever.
Not true. Not for the home gunsmith, but changing the barrel is possible. Quoting John Barsness:
"But the desire to change the chambering of your rifle every few months, whether because of boredom or the introduction of a new “Wonder Cartridge,” is far from universal, and if you happen to shoot enough to wear out a Sauer or Mauser barrel then you can also probably afford to send the rifle back to Germany for a replacement. (A new barrel probably won’t cost any more than having a typical American gunsmith screw in a new barrel, and probably won’t take any longer, either.) Pressing the barrel into the action also results in a very stiff connection, another reason for the accuracy of both rifles."
https://www.americanrifleman.org/articles/2014/3/20/german-resurgence-mauser-12-and-sauer-101/
