After setting the climate in advanced options to "Alpine - 900m" and going back to the "new game" dialogue the chosen climate preset is "dry", not "temperate" as it was before.
When I choose "temperate" then, the climate preset is not "Alpine - 900m" anymore and also reset to "temperate".

The only workaround seems to use the main temperate setting - with any map creation mod - start the game and change the preset to "Alpine - 900m" when loading the game the next time.