There's definitely a H/W mod option for the VX-8r for MARS type use.
Yep, I had done it to my original 8R. When I got it back from Yaesu after the 8DR upgrade, they put the resistor back :)
http://www.kb2ljj.com/data/yaesu/VX-8R.htm
This claims to document a soft mod that's accessible via magic key combinations but I don't know that it necessarily involves memory that's exported in a clone
I forgot about this entirely until just now. I had tried it once upon a time and didn't get it to work.
If, however, it does, then maybe we could use that to figure out where (if at all) it's triggered in the memory. The string you type in (AH029) is, by the way, the model identifier that the PC and radio exchange during a clone. So, we should know it for other radios as well, such as the VX3. Might be worth a shot.