Picasa is very unlikely to be changing the RAW file itself. What you’re probably seeing is a common RAW-viewer behavior: first it displays the JPEG preview embedded in the RAW file, then it replaces that with its own rendered interpretation of the RAW data.

That second view can look different because a RAW file is not really a finished image. A usable preview requires demosaicing and tone/color decisions, so there isn’t a single true “unedited RAW look.” In many cases, the camera’s embedded JPEG preview actually looks more polished than a basic RAW rendering.

So the change you see is most likely preview-switching, not destructive editing. Based on the answers provided, there’s no indication that Picasa can be configured to show only a pure, untouched RAW image—because such a direct view isn’t really meaningful in the same way as a JPEG. If you specifically want the camera-made look, you’d want a viewer that shows the embedded JPEG preview rather than re-rendering the RAW.