I fixed the link (typo missing s). Replacing the atmega8u2 using DFU mode is quite safe, you can always reprogram it with Arduino-usbserial.hex to recover the normal Arduino operation. I'm suggesting trying the MIDI firmware because I think its simpler to use than the serial solution. If you run into problems just drop me an email on darran [at] hunt [dot] net [dot] nz.
Cheers,
Darran.