It's not just Toyota, most DVD-based Nav systems work the same way. I had an Acura MDX and when the DVD drive went bad the Nav and audio system would reboot over and over. Thankfully the climate controls were separate from the Nav system. I think the integrated climate controls are my big...
The climate controls should be separate. There's so little benefit to integrating them into the nav unit. But I'm not surprised that any functions the Nav normally does would be broken if the unit can't boot.
There's no way I'm aware of to modify the system. If the DVD is missing or won't load, you're boned.
If I could hack the Nav system there are a bunch of changes I'd make. However it's running QNX and uses signed binaries. It's likely possible in theory but it would require significant...