Why would a new pin be a mistake?
A collector of WW2 items would or could believe it is a fake. "New pin = fake" "over cleaned and polished to look "new" = Fake" Collectors (especially those who collect war time items) want original condition, no matter how bad it is.
Preservation by removing any active red rust is acceptable, so long as it is not "restored" to new condition. It would not be too difficult to copy the handle, giving credence to the "its fake" belief.
If mine, at
most I might try peening the pin - provided I had the correct tools - including a rivet setter to keep the pin heads rounded. Even if I had the proper tools, I would be far more likely to leave it as-is, and display it in a shadow box, or something, and get a current production friction folder (or slipjoint) for use.
If you want a friction folder user, there are plenty of friction folders besides MAM, SVORD, and Opinel on the market at "reasonable prices".
("reasonable price" is always based on income, and the "comfort zone" for how much person is willing to spend for that item.)