Hi Amadeus, normally the K31 has a great trigger. I haven’t shot many, but they all were well above average for milsurps.
Concerning the blueing, I wouldn’t do it. They are mostly a bit worn due to the intensive training the Swisssoldiers got for all their young adults’ lifes, and it really is part of the beauty of these rifles.
But that is just a very personal opinion, and is worth what it is.
Enjoy the oldie.