As for damage to the car, I doubt it, but am not willing to try it on my MS either. Most DC-DC converters like this have a current limit function that will keep any damage from happening.
For example, the Prius HV to 12V, DC-DC converter is rated at up to 100A. Several Prius owners, including myself, have installed AC inverters on the 12V line with large connections to get backup power up to 1000W. Turns out the Prius with inverter has efficiency comparable to one of the Honda inverter generators and a gas tank that can run the output for days. If the DC-DC converter in the MS is of a comparable size to the Prius, then the HV battery in the MS would also support this kind of backup power for days. This is just a thought for me; I have other backup power solutions.