The guys from Magic Lantern have been able make the old EOS 50D (a 5-year-old camera, a relic by today’s standards) capable of recording RAW video through Magic Lantern software.
And here’s the video proof from the folks at EOS HD.
Would something like this void the warranty? Well, DIY Photography asked this to three manufacturers (Canon, Nikon and Panasonic) and, surprisingly, Canon’s answer was no, you don’t void the warranty.
An entirely different thing, however, is if the camera is damaged by the use of illegal or unsupported software. In this case, Canon would repair the camera, but you’d have to go pick it up.
For example, Canon stated the following (which honestly was not very clear, in my opinion):
Nothing has been stated about voiding the warranty. Some repairs are covered and others are not. For example, the repair of a failure in the buttons during the warranty period would probably be covered if the camera shows no signs of incorrect use. However, the same issue would likely not be covered in the case of a camera with evident signs of misuse or damage.
Canon mentioned nothing about the EOS-1 cameras. Based on what the article states, it seems Canon may take legal action against people who publicly spread the use of unauthorized firmware for EOS-1 units, so this may be the reason that software for this kind of cameras is not known to exist.