Thanks for the reply Cameron. Yes it worked when I used the installer.
Some remarks.
The Saab 340 works surprisingly well in XP12. Like, I was genuinely surprised. The sound effects appear even better than in XP11 (maybe imagination), autopilot seems to work well and I could fly it without real problems. The throttle levers sometimes get stuck but that was already a problem in XP11.
All in all this is now my favorite "copied" XP11 plane in XP12 and works much better than all others (Zibo, FJS 732 etc).
The only real problem is cockpit lighting. I could mitigate that by increasing blrightness on several cockpit dds files (basically I just used "Auto Adjust Colors". attached screenshots, one under good and another under extremely bad lighting conditions in the Arctic). It's only a hack but it can be done in like 10 minutes and allows me to enjoy this plane and fly it in XP12 already.
How hard would it be to make a pure graphical update that only adresses the cockpit brightness?