This is Roland's most inexpensive 4 octave MIDI controller, but this mod will probably work quite well on most Roland keyboards and controllers.  My biggest complaint with Roland gear is the silly  one piece pitch bend and modulation joystick.   I prefer to have a seperate mod wheel... and one that's NOT spring loaded, as well.  I often like to crank up my modulation and leave it on for a while, which is impossible with Roland's design.   This is an ultra-simple mod, but I found it to make my synth much more usable for me.  

     I opened up the controller and measured the resistance of the modulation portion of the joystick.  It fluctuates between about 56K and 0 ohms (with 0 ohms giving full modulation).  The two wires in question come out of the center of the joystick, and were quite obvious to find.  They were blue and yellow in this particular unit.  I cut the two wires and routed them through one side of a DPDT switch.  The two center contacts of the switch reconnected to the original destination.  On the other side of the switch, I used a 50K pot and a 10K trimmer in series to simulate the original mod lever.  You simply adjust the trimmer until the resistance is exactly the same as the original unit.  Here's a little pic of exactly how I wired it.  Now it's possible to use the new mod source, or the original joystick.  I can also set the pot and quickly switch between the two for some interesting effects.  I suppose a DP3T switch with On-On-(On) contacts would work best... you could then tap the momentary side to quickly jump from the stock joystick to the pot.

     I've also added a number of pushbutton momentary switches to the front controller.  They connect directly to a 1/4" TS jack on the rear of the controller.  Pushing the button shorts the two contacts on the 1/4" jack.  I use these pushbuttons to connect to "footswitch" jacks of gear that is far away from my keyboard table.  I will ocassionally use these buttons to control Start/Stop of my MMT-8, or to toggle between "on" and "bypass" on some of my effects units.  I've found these to be VERY handy.  Also, since these jacks short the tip and sleeve, I also use them as a "mute" function.   For example... I sometimes run my analog kick module's output into a jack multiple.  One wire is used to connect the multiple to the mixer input, and a second wire connects the multiple to the pushbutton. When I push the button it shorts the kick's output to ground, muting the signal. Be sure to use this technique only if the output section of the sound source is tolerant of being shorted to ground.