Found a solution to remote switch 12Step presets automatically and by another MIDI footswitch in Ableton Live:
For both remote preset switching methods create a new MIDI track, I call it "12Step". Set the MIDI input to none, the MIDI output to "12Step Port 1", the MIDI channel does not matter, the 12Step receives any channel.
Create an empty/dummy MIDI clip. Set it's Program Change to the desired number. E. g. 12Step preset 17 is PC Message 17.
Now the 12Step's preset will change accordingly when you launch the scene containing the MIDI clip.
For using another MIDI footswitch (in my case an iCon G-Board), create a MIDI clip for each preset and create a "shortcut" for it in Live's MIDI Mappings. For using the footswitch only and to prevent auto switching I moved the Dummy MIDI clips down in the scene slots, after the last scene containing loops/stuff to play back.
If anyone has a more elegant solution for this, please let me know.