The MT-100 was the first Casio keyboard I got on Ebay. It basically has the same hardware of the MT-68 or the legendary MT-400 V, just with a few lesser developed functions and a 5-band equalizer.
Optically, the modifications differ strongly from my later ones, but they are very comfortable and sturdy. I built in the following functions:
Mute switch for bass and chords
Mute switch for all singular drum sounds in external casing
Additional "tempo fine" controller
Sustain values of bass and chord sounds can be altered by switch