(...) but each time loading it on the camera, it displays the value last set by me on the camera.
This happens despite that I have set "save params" to off.
That's because the CHDK loads parameters you have previously set on camera. These settings are stored somewhere in CHDK folder (DATA or something - I'm not sure now).
The scripting menu has an entry called "Load default param values" that will take care of this if you click on it.