To reinforce what Marco said, I recently found a program called "Softjump" that could enable wider-band TX on the FT-857 purely with CAT commands! I tried and tried and it wouldn't work both with his code and my own code derived from his CAT commands. I was going to contact the author but when I looked at his QRZ page, he stated there that Yaesu evidently removed those specific undocumented CAT commands back in the 2004 timeframe. :-( So, though I *do* think it would be worth adding this interactive method to read/write the Yaesu radios like we can with Kenwood, we should probably get the Clone approach down solid first.
Btw, lots of good FT-8x7 information here: http://www.kb2ljj.com/data/yaesu/ft-857.htm
From the information I have, undocumented peek and poke cat commands still works but yeasu blocked the possibility to write on the configuration byte (at address 4 and 5) on newer radio to avoid "softjump" tampering.
If you are a brave you can try to write on the label of one of the memories to see if the poke command still work, I suggest you don't write on current memory channel as seems yeasu radio don't like this. You can calculate the address using info on http://www.webalice.it/famiglia.pagni/default.html (in the hope they are right).
BTW I widebanded my 857 with softjump lots of years ago.
73 de IZ3GME Marco