The hacking process is relatively safe. The main concern for you is choosing one of the more "stable" hacks for you documentary work. Some of the "less stable" hacks can freeze up during shooting forciing you to restart your camera. But there are a lot of "safe" ones out there. Check the personal-view.com site for more info.
As with any firmware upgrade, the camera must not power down until the firmware is fully loaded. Use a fully charged Panasonic battery - do NOT risk using a 3rd-party battery or main adapter.