Try +set gl_texturemode gl_linear instead then. And I mean on the command line, when starting the application, not the ingame console.
Good! At least *that* worked. When loading game now with empty savegame folder and default config file, the game looks much better when switched to hardware renderer!
But there is more.. I have now succesfully saved and restored my games a few times, by specifying a different user path (outside of the game dir) in the launcher app. Doesnt work all the time, but at least the game now loads in 80% of cases.. Was probably just a case of bad coincidence before?
I can also save my config file, but it wasnt automatically loaded. Therefore I copied it over to my custom user dir and renamed it to user.cfg. This works! Config is now autoloaded and thanks to that added launcher option, the game looks nice, too. I'm pretty sure this is not the way I should have done it, but it works now, so many thanks for helping me out.
In case anyone didnt follow this:
1) add custom startup command in launcher: +set gl_texturemode gl_linear
2) add custom user dir in launcher to save your games to
3) copy config.cfg to user.cfg in custom save dir (see 2)