OK, here's the first one I found, gives you rx/tx 140-174 MHz and rx/tx
420-470 MHz:

DISCLAIMER:  PERFORM THIS PROCEDURE AT YOUR OWN RISK.  THE POSTER(S) OF
THIS PROCEDURE ASSUME NO LIABILITY, AND THIS PROCEDURE IS POSTED FOR
GENERAL INFORMATION ONLY.  THE FT-51R RADIO IS NOT FCC-TYPE ACCEPTED FOR
TRANSMISSION OUTSIDE OF THE AMATEUR RADIO FREQUENCIES.  THIS MODIFICATION
ENABLES TRANSMISSION ON FREQUENCIES OUTSIDE OF THE AMATEUR RADIO BAND, AND
IS LEGAL FOR THOSE INDIVIDUALS WITH MARS/CAPS CERTIFICATES.  THIS
MODIFICATION REQUIRES THE USE OF A LOW POWER FINE TIP SOLDERING IRON. 
INDIVIDUALS WHO ARE NOT EXPERIENCED WITH SOLDERING OF SURFACE MOUNT
TECHNOLOGY SHOULD NOT ATTEMPT THIS MODIFICATION, YOU COULD RUIN YOUR
RADIO.

1. Remove the battery pack from the radio.

2. Remove the four screws directly beneath the battery pack on the radio.

3. Remove the two screws holding the contact portion of the battery compartment.

4. Remove the screw and battery pack release lever.

(the following steps make removal of the battery holding compartment easier)

4. Remove the four screws on the bottom portion of the back of the
cabinet. Carefully remove the two halves of the radio.  Pay attention to
the gasket as you are seperating the cabinet.

5. Remove the battery pack holding compartment.

The section you will know be working with is directly underneath the
battery pack holding compartment (behind the touch tone pad).  

6. There is a ribbon cable connected to the control board.  You can leave
the ribbon cable attached if you're a GOOD solderer, or you can release
the two little black levers on each side of the ribbon cable and CAREFULLY
slide the ribbon cable out of the socket and hold it back towards the case
with a piece of tape.  Be careful not to put a bend in the ribbon cable or
pierce it.

7. Locate a set of etched jumpers on the pc board.  They are located
adjacent to the bend in the ribbon cable.  They are not marked, and are
situated as follows (o-o indicates closed, o o indicates open):
 

      JP1001   o-o
                     o o JP1005
      JP1002   o o
                     o o JP1006
      JP1003   o o
                     o-o JP1007
      JP1004   o-o

8. Using solder wick or your preferred method of solder-removal, carefully
remove the jumper for JP1007.  This enables the 134-174, 420-470 MHz
transmit.

9. Reassemble the radio, remembering to reinstall the gasket, and to
carefully reinsert the ribbon cable if you removed it from the socket, and
fasten down the little black socket locks.

10.  Press the MHZ /\ and MHZ \/ buttons simultaneously while turning the
power on to the radio.  This enables the modification.

Some notes:  I experimented with removing JP1004, and it had no apparent
effect.  I did not experiment with any of the other jumpers except
JP1007.  There still may be 800 MHz receive buried some where in the
radio, the Japanese version has 800 MHz receive.  An earlier posting of
mine indicates four large resistors (well, non-surface mount) connected
between various microprocessor and memory pins, clearly an add-on. 
Experimentation with removing these produced no effect, HOWEVER, this was
prior to my discovery of the JP1007 mod.  I've played with the radio
enough now, and don't want to push my luck, so let's let someone else try
to find out if there are any more secrets buried in this fine piece of
gear.

-- 
Marc B. Grant
marcbg@metronet.com
Amateur Radio N5MEI