Welcome to the forums. Just so you know, this forum is about putting computers in cars, not about headunits. That being said, the short answer to your question is no.
You might be able to pull the headunit apart, solder on a JTAG interface to whatever controller chip they have inside, write a new program for it and flash it... but that's extremely unlikely. I'm willing to bet most companies lock the chips before they ship them. That's assuming you know what kind of interface the chip has to the rest of the radio, which there is no way of knowing. Heck, even theoretically it's a nightmare. Just go for a carpc, you can put whatever OS on it you want